bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Chromium on the Hall-Petch Coefficient in Ferritic Steel
Authors: Hironaka Akira , Nakada Nobuo , Tsuchiyama Toshihiro , Takaki Setsuo
Published: January 2012

In ferritic stainless steels, the amount of Cr is moderately controlled to have good corrosion resistance in applied environment. However, it also affects the yield strength of ferritic stainless steels through solid solution strengthening and grain refinement strengthening. Until now, some researches have been performed using commercial stainless steels but the obtained results contain the effect of solute interstitials (C and N). In this paper, the influence of Cr on the above both strengthening mechanism was discussed by using interstitial free ferritic stainless steel in which carbon and nitrogen are completely fixed as Ti(C,N). A previous paper has reported that the addition of chromium gives different influences to the Hall-Petch coefficient depending on the amount of Cr. However, our research has reveals the fact that the change of Hall-Petch coefficient is not due to the effect of chromium but due to small amount of carbon which exists as an impurity in ferritic stainless steels. It was concluded that chromium itself does not give any influence to the Hall-Petch coefficient of ferritic iron.
Microstructure Evolution and Softening Processes Occurring during Annealing of Hot Deformed Ni-30Fe Austenite
Authors: Hodgson Peter , Cizek Pavel , Beladi Hossein , Taylor A.S.
Published: January 2012

The current work investigates the microstructure evolution and softening processes that take place during annealing of an austenitic Ni-30Fe model alloy subjected to hot deformation in the dynamic recrystallization (DRX) regime. The substructure of the deformed matrix grains largely comprised organized microband arrays, though that of the DRX grains consisted of more random, complex subgrain/cell arrangements. This substructure disparity was also reflected by the distinct difference in the mechanism of post-deformation softening taking place during annealing of the deformed matrix and DRX grains. In the former, the recrystallization process took place through nucleation and growth of new grains fully replacing the deformed structure, as expected for the classical static recrystallization (SRX). The corresponding texture was essentially random, in contrast to that of the DRX grains dominated by low Taylor factor components. The microbands originally present within the deformed matrix grains displayed some tendency to disintegrate during annealing, nonetheless, they remained largely preserved even at prolonged holding times. During annealing of the fully DRX microstructure, a novel softening mechanism was revealed. The initial post-dynamic softening stage involved rapid growth of the dynamically formed nuclei and migration of the mobile boundaries in correspondence with the well-established metadynamic recrystallization (MDRX) mechanism. However, in contrast to the deformed matrix, SRX was not observed and the sub-boundaries within DRX grains rapidly disintegrated through dislocation climb and dislocation annihilation, which led to the formation of dislocation-free grains already at short holding times. Consequently, the DRX texture initially became slightly weakened and then remained largely preserved throughout the annealing process.
The Influence of Austenitization Temperature on the Mechanical Properties of a Prehardened Mould Steel
Authors: Hoseiny Hamed , Caballero Francisca G. , San Martín David , Capdevila Carlos
Published: January 2012

The many practical difficulties and longer lead time with heat treatment of mould steels after machining have led to increased demand for steels in prehardened condition, typically ~ 40HRC. At this hardness the steel possesses an optimal combination of high strength and machinability. The steels used for moulds require a wide range of demanding properties, among which high enough strength and toughness are the primary necessities in order to resist any deformation and dimensional change in mould during use. Uddeholm Impax HH which resembles the modified AISI P20 has been widely used for moulding of plastics and die-casting of low melting temperature metals. The common hardening process for Impax HH is conventional quenching and tempering. Hence, investigating the effect of hardening parameters on the required properties upon this steel grade is beneficial in improving it for better performance as a prehardened mould steel. In the present work, the effect of changes in austenitization temperature and consequently the prior austenite grain and martensite packet sizes on the tensile properties and impact toughness of Uddeholm Impax HH at the hardness of ~40HRC is studied. The results have shown reduction in impact toughness but no considerable change in yield and ultimate tensile strength upon increasing the austenitization temperature.
Sintering Performance and Mechanical Properties of Titanium Compacts Prepared by Spark Plasma Sintering
Authors: Izui Hiroshi , Kikuchi Genki
Published: January 2012

Titanium alloys were produced by blended elemental powder metallurgy (P/M) method. We focused on the effect of alloying elements (Fe, Mo, and Al) on the consolidation and mechanical properties of Ti compacts prepared by spark plasma sintering. The effects of amount of alloying elements and sintering temperature on the relative density and tensile properties of Ti compacts were investigated. The addition of β-stabilizing elements (Fe and Mo) significantly improved the densification of Ti compacts, where the relative density ratio of Ti-5 wt% Mo specimen became higher than 99.9 %, and Ti-5 wt% Fe specimen higher than 99.0 %. On the other hand, the addition of Al as α-stabilizing element led to improve the relative density of Ti-5 wt% Al compact with higher than 99.9 %. The tensile property for sintered Ti-5 wt% Mo compact had the highest elongation of 16 %. It will be discussed the microstructures and tensile property of the compacts.
Work Hardening Mechanism in Soft Particle Dispersion Ferritic Steel
Authors: Nakada Nobuo , Murakami Masahiro , Tsuchiyama Toshihiro , Takaki Setsuo
Published: January 2012

The work hardening behavior was investigated in ferritic steels containing hard particles or soft Cu particles with various volume fractions and particle diameters, and then the effect of plastically deformable soft particles on the work hardening was evaluated in terms of the accumulation of GN dislocations. The amount of work hardening and dislocation density increased with an increase of volume fraction of dispersion particles and a decrease of particle diameter in hard particle dispersion steel. On the other hand, in soft Cu particle dispersion steel, the effect of volume fraction and particle diameter on work hardening behavior was relatively small. TEM observation suggested that stress relaxation around particle takes place by plastic deformation of Cu particle itself. In order to consider the effect of plastic deformation of Cu particles on accumulation of GN dislocations, "particle plastic accommodation parameter" was proposed to modify the Ashby's work hardening theory. As a result, the amount of work hardening was successfully predicted for both the hard and soft particle dispersion steels
The Role of Notches on Fatigue Life of TWIP Steel in the HCF Regime
Authors: Niendorf Thomas , Klimala Peter , Maier Hans J. , Frehn Andreas
Published: January 2012

The present paper reports on the fatigue response of a commercial high manganese steel that features the twinning-induced plasticity (TWIP) effect in the high-cycle fatigue (HCF) regime. Specifically, attention was paid to the influence of the degree of pre-deformation and notches on the damage initiation and propagation in the TWIP steel studied. As monotonic pre-deformation significantly increases the fraction of twins and concomitant the strength of the steel, the fatigue properties and notch sensitivity are altered drastically. A thorough experimental approach including mechanical testing and microstructural characterization was employed to shed light on the microstructure-mechanical properties-relationships in order to deepen the understanding of the critical damage mechanisms. The current study clearly lays out that competing mechanisms effect the fatigue response of the TWIP steel, i.e. pre-deformation leads to strengthening but also induces damage. Since both effects evolve differently upon pre-deformation, fatigue performance can be optimized by appropriate amounts of pre-deformation.
Effect of Static Aging on Mechanical Properties of an 18Cr-8Ni-W-Nb-V-N Stainless Steel
Authors: Nikulin Ilya , Kaibyshev Rustam
Published: January 2012

The interrelations between microstructure, precipitation and mechanical properties of the 18Cr-8Ni-W-Nb-V-N austenitic stainless steel were examined under long-term aging at 650°C. It was shown that aging leads to decreasing strength characteristics with increasing aging time despite the fact that hardness tends to increase. In none-aged condition the present steel exhibits superior impact toughness of about 255 J/cm-2. This values decreases gradually at the early stage of the aging. After 1000 hours exposure the impact toughness is 195 J/cm-2 and decreases sharply to 135 J/cm-2 at 3000 hours. However, an evidence for ductile fracture was found even after long-term aging. Degradation in impact toughness and mechanical properties with aging is discussed in relation to microstructure evolution, precipitations of the secondary phase and fracture mechanisms.
Cutting Properties of Austenitic Stainless Steel by Using Linear Polarized CO2 Laser without Assist Gas
Authors: Ozaki Hitoshi , Mima Takahito , Kawakami Hiroshi , Suzuki Jippei
Published: January 2012

Recently, laser cutting is used in many industries. Generally, in laser cutting of metallic materials, assist gas and its nozzle are needed to remove the molten metal. However, because of the gas nozzle should be moved closer to the position about 1 mm from the surface of a workpiece, it is thought that existence of the nozzle causes lack of flexibility of laser cutting. Therefore, the new cutting process, Assist Gas Free laser cutting (hereafter, called as AGF laser cutting), has been developed and investigated about cutting properties in our laboratory. In this process, the pressure at the bottom side of a workpiece is reduced by a vacuum pump, and the molten metal can be removed by the air flow caused by the pressure difference between both sides of the specimen. On the other hand, when cutting of metallic materials with a linear polarized laser is performed, it is known that the cutting kerf might slant. This phenomenon is also observed in AGF laser cutting. In the present study, cutting properties of austenitic stainless steel by using liner polarized CO2 laser in AGF laser cutting was investigated. Cutting speed and direction were varied in order to study the effect of these parameters on cutting properties. As a result, when the angle formed by the cutting direction and the polarized direction of laser was parallel, the kerf slant could be depressed, and the critical cutting speed could be the fastest in any other cutting direction.
Recrystallization Behaviour of Nb and Ti+Nb Added Ferritic Stainless Steels
Authors: Park Ji Eon , Park Soo Ho
Published: January 2012

The effect of alloying elements and rough rolling condition on the microstructure evolution of ferritic stainless steel has been investigated in order to understand the recrystallization and precipitation behaviour during hot rolling. In the present study, a series of high temperature compression tests with plane strain deformation mode were conducted for Nb added and Ti+Nb added ferritic stainless steels. Compression tests then were subjected to various conditions of deformation temperature, reduction ratio and holding time. After the tests, EBSD mapping and SEM observation were performed to analyze the recrystallization and precipitation behaviour. Nb added and Ti + Nb added steels show an increasing tendency of recrystallization with an elevation of deformation temperature, holding time and reduction ratio. An increase of holding temperature and holding time enlarges the recrystallized regime due to a decrease of activation energy for recrystallization and a growth of recrystallized grain. A higher reduction ratio also increases the recrystallized regime due to a rise of stored energy for recrystallization. Nb added steel, however, is more resistant to recrystallization because most of Nb (C, N) particles in Nb added steel are finely dispersed in the matrix.
Potential of Hot Rolled Dualphase Steel from Compact Strip Production CSP® in Automotive Applications
Authors: Reip Carl Peter , Klinkenberg Christian , Tong Long Chang , Hora Pavel
Published: January 2012

Industrial thin slab casting and direct rolling processing started in 1989 with the world’s first CSP® plant at Crawfordsville (USA). Since this time CSP® and competing thin slab casting and direct rolling concepts have been developed to a standard process for hot strip production [1]. Typical features of the CSP® process are the homogeneous structural and mechanical properties all along the strip. Direct hot rolling of thin slabs may be followed by a well defined cooling pattern to produce hot strip from high strength multiphase steel, like dualphase (DP) grades, on the runout table. These steel grades are characterized by a favorable combination of strength and ductility based on hard martensitic particles embedded in a ductile ferritic matrix. This paper highlights the mechanical properties of hot rolled DP steel from CSP® production. To this purpose, multiple tests and modeling have been applied to determine e.g. r-values, forming limit curves and yield locus. In addition, forming simulation as well as laboratory and industrial deep drawing tests have been performed.
Volume Change Associated to Carbon Partitioning from Martensite to Austenite
Authors: Santofimia M. J. , Zhao Lie , Sietsma Jilt
Published: January 2012

Annealing of martensite/austenite microstructures leads to the partitioning of carbon from martensite to austenite until the chemical potential of carbon equilibrates in both phases. This work calculates the volume change associated with this phenomenon using theoretical models for the carbon partitioning from martensite to austenite. Calculations are compared with experimentally determined volume changes. This comparison reveals that in the case of steels with higher contents of austenite-stabilizing elements, reported volume changes are satisfactory predicted assuming a low mobilily martensite/austenite interface. In the case of a steel with lower additions of austenite-stabilizing elements, experimentally measured expansions are considerably larger than predicted ones. The large measured volume expansions probably reflect the decomposition of the austenite.
Mesoscopic Modeling of Discontinuous Dynamic Recrystallization: Steady-State Grain Size Distributions
Authors: Piot David , Damamme Gilles , Montheillet Frank
Published: January 2012

A simple mesoscale model was developed for discontinuous dynamic recrystallization. The material is described on a grain scale as a set of (variable) spherical grains. Each grain is characterized by two internal variables: its diameter and dislocation density (assumed homogeneous within the grain). Each grain is then considered in turn as an inclusion, embedded in a homogeneous equivalent matrix, the properties of which are obtained by averaging over all the grains. The model includes: (i) a grain boundary migration equation driving the evolution of grain size via the mobility of grain boundaries, which is coupled with (ii) a dislocation-density evolution equation, such as the Yoshie–Laasraoui–Jonas or Kocks–Mecking relationship, involving strain hardening and dynamic recovery, and (iii) an equation governing the total number of grains in the system due to the nucleation of new grains. The model can be used to predict transient and steady-state flow stresses, recrystallized fractions, and grain-size distributions. The effect of the distribution of grain-boundary mobilities has been investigated.
Influence of Matrix Structure and Hard Carbide on Abrasive Resistance of Steel Plates
Authors: Ueda Keiji , Ishikawa Nobuyuki , Murota Yasuhiro
Published: January 2012

The microstructure of abrasion resistant steel plate usually consists of as quenched martensite, because harder matrix structure improves abrasion resistance of a steel plate. However hard martensitic material has lower formability, which is the important material property for fabricating machine parts. In this paper, a new type of abrasion resistant technique for steel plate is introduced. The steel provides good combination of high abrasion resistance and excellent formability without increasing hardness. The key technology to balance abrasion resistance and formability is the microstructural control of the ferritic matrix structure with dispersed extremely hard carbide particles. Basic research of abrasion mechanism revealed that abrasion resistance is strongly affected by the kind of carbides and the dispersed condition.
Improved Performance in Aerospace Structures with Ti and Ni Metal Matrix Composites
Authors: Testani Claudio , Tului Mario
Published: January 2012

The external structures of supersonic vehicles are exposed in several critical regions to temperatures that could reach 1000°C. This limit is higher than any safe operative service not only for titanium alloys but also for commercial nickel superalloys. The simplest way to improve titanium and nickel matrices temperature behavior (i.e: strength and fatigue resistance) is to introduce a strengthening phase in its matrix. These class of materials are known as: Metal Matrix Composites (MMC). It is possible reinforce both titanium and nickel superalloys by mean of high temperature resistant ceramic fibers.
Crack Growth Behavior in ATI 718Plus® Alloy
Authors: McDevitt E. T. , Oppenheimer S. M. , Kearsey R. M. , Tsang J.
Published: January 2012

ATI 718Plus® alloy is a new, cast and wrought, Ni-base superalloy with a maximum use temperature approximately 55°C higher than alloy 718. The mechanical properties have been well characterized by turbine engine OEM’s and the alloy has been specified for use as static components and blades in gas turbine engines. Broader use of ATI 718Plus alloy in engine disk applications requires detailed understanding of the damage tolerance under creep and cyclic loading conditions. The results of a large testing program to evaluate the crack growth behavior of ATI 718Plus alloy at temperatures between 649°C and 704°C under conditions of fatigue, dwell-fatigue, and creep are presented. Crack growth rates in ATI 718Plus alloy in this temperature range are lower than alloy 718 and comparable to Waspaloy under non-dwell-fatigue conditions, and comparable to alloy 720 in dwell-fatigue tests.
Influence of Stacking Fault Energy on Creep Mechanism of a Single Crystal Nickel-Based Superalloy Containing Re
Authors: Tian Su Gui , Qian Ben Jiang , Su Yong , Yu Hui Chen , Yu Xing Fu
Published: January 2012

By means of calculating stacking fault energy (SFE), measuring creep properties and contrast analysis of dislocation configuration, an investigation has been made into the influence of the stacking fault energy on the creep mechanism of the single crystal nickel-based superalloy. Results show that the alloy at 760¡æ has a lower stacking fault energy (SFE), and the SFE of the alloy increases with the temperatures. The deformed mechanism of the alloy during creep at 760¡æ is the cubical γ′ phase sheared by <110> super-dislocation which may be decomposed to form the configuration of (1/3)<112> super-Shockley partials dislocation plus the superlattice intrinsic stacking fault (SISF). The deformed mechanism of the alloy which possesses the higher SFE at 1070¡æ is the screw or edge super-dislocation shearing into the rafted γ′ phase. The SFE of the alloy at 980¡æ is intervenient between the ones of 760¡æ and 1070¡æ, the deformation mechanism of the alloy during creep is the rafted γ′ phase sheared by <110> screw and edge super-dislocations which may be decomposed into the configuration of (1/2)<110> partial dislocation plus APB.
Effect of Surface Hard Layer and Forging Conditions on the Resistance of Plastic Deformation of Hot Forging Tools
Authors: Minami Akihiro , Tabaru Yoshihiro , Marumo Yasuo , Ruan Li Qun , Saiki Hiroyuki
Published: January 2012

Tool damages including plastic deformation and wear are affected by forging load, thermal load and frictional slide applied to tool surface. Plastic deformation of forging tools proceeds in the tool corer owing to elevated temperature, high contact pressure and severe frictional slide. Hard layers on the tool surface increase plastic deformation resistance and thermal resistance. The optimal design of hard layer structure reduces the tool damage and improves tool life. Temperature and equivalent strain of forging tools are influenced by friction shear factor, contact thermal conductance and contact time between the tool and the workpiece. At the friction shear factor of less than 0.4, equivalent strain of the tool is reduced. At the friction shear factor of approximately 0.4 or greater, equivalent strain increases sharply and concentrates in the vicinity of the surface hard layer. This tendency becomes more significant when the contact time between the tool and the workpiece increases. Equivalent strain is reduced by low workpiece temperature.
Oxidation Resistance and Self Hardening of CrAlN/BN Nanocomposite Coatings
Authors: Nose Masateru , Watanuki Tomohiro , Kawabata Tokimasa , Hatano Yuji , Matsuda Kenji , Ikeno Susumu
Published: January 2012

CrAlN/BN nanocomposite coatings were deposited on mirror-polished silicon wafer and high-speed steel (HSS) substrates using reactive cosputtering, i.e., pulsed dc and rf sputtering of CrAl and h-BN targets, respectively. Further, the oxidation resistance of the obtained coatings was investigated. The CrAlN/BN coating exhibited superior oxidation resistance properties when compared with those of the CrAlN coatings; after annealing the sample at 800 °C in air for 1 h, the plastic hardness value of the CrAlN coatings decreased to 50% of the as-deposited hardness value; in contrast, the CrAlN/BN coatings exhibited self-hardening phenomena from 700 to 800 °C in the range of 5 to 30%. In particular, the CrAlN/18 vol% BN coatings showed an increase of approximately 30% in hardness values, and a maximum hardness value of approximately 50 GPa was reached after annealing the sample at 800 °C in air. The plastic hardness value hardly changed when the sample was annealed up to 800 °C in nitrogen and argon; this result was contrary to the result obtained for the sample that was annealed in air. The radiofrequency glow discharge optical emission spectroscopy (rf-GD-OES) analysis of the CrAlN/18 vol% BN coating annealed in air revealed that the coating has an oxide layer deposited on the surface to a depth of ~200 nm. Conventional transmission electron microscopy (TEM) observations of the same coating indicate that the columnar structure was disrupted by a thin layer (30–40 nm) of the coating annealed in air. The indentation hardness value of the annealed coating was measured using Ar ion sputtering before and after etching of the annealed surface. Subsequently, when the oxide layer was etched to a depth of 200 nm from the surface, the hardness value decreased from approximately 48 GPa to 43 GPa; this result was similar to the results obtained for the as-deposited coating.
Effect of Diffusion Condition for Aluminizing on TiAl Based Alloy
Authors: Sasaki Tomohiro , Yagi Takahiro , Watanabe Takehiko , Yanagisawa Atsushi
Published: January 2012

Diffusion treatments of TiAl-based alloys (49.1 at% Al) aluminum coated by thermal spray were carried out at the temperature range of 700°C-1100°C. The influence of the diffusion condition for the formation of intermetallic phases in the coating has been investigated. In the initial stage of diffusion treatment, TiAl3 was formed on the outermost surface by the diffusion between liquid aluminum and the substrate. In addition, an intermediate layer comprised of Ti2Al5 (at 1100°C), TiAl2 and Al diffused layer (Al-rich TiAl) was confirmed under the outermost layer. The maximum thickness of TiAl3 during the initial stage increases as the diffusion temperature decreases. In addition, the shape of TiAl3 layer was dependent on the diffusion temperature; the outermost layer without pores was confirmed at the temperature of 700°C. TiAl2 and Al-rich TiAl developed by solid-state diffusion from TiAl3 layer following a parabolic low. The activation energies for growth have been calculated to be 194 kJ/mol for TiAl2 and 292 kJ/mol for Al-rich TiAl.
Orientation Gradients in α-Fibre Grains of Cold Rolled IF Steels
Authors: Gobernado Patricia , Petrov Roumen H. , Moerman Jaap , Barbatti Carla , Kestens Leo A.I.
Published: January 2012

The plastic behavior of the <110>//RD orientations, and specially that of the {001}<110> orientation, under severe cold reductions is addressed. Based on the orientation dependence of the stored energy, the {001}<110> orientation is known to lack from structured misorientation gradients and significant dislocation storage after plastic deformation which makes the former orientation not particularly prone to enhancing the recrystallization process. Recent evidences, however, indicate that {001}<110> orientation plays a relevant role in the origin of {h11}<1/h,1,2> orientations (predominantly {311}<136> and {411}<148> orientations) observed in the recrystallization texture of severely deformed IF steels. The complete understanding of the development of the recrystallized {h11}<1/h,1,2> orientations in IF steels is, therefore, of relevance as it deteriorates the optimum γ-fibre texture required for deep-drawability applications. The plastic instability of {001}<110> grains in a cross-rolled IF steel is evaluated in the present work. The extensive characterization of the deformed substructure along with partially recrystallized data confirmed the oriented nucleation origin of {h11}<1/h,1,2> orientations from deformed {001}<110> grains. Innovative crystal plasticity calculations accounting for the position of the grain boundary plane suggested that the recrystallized {h11}<1/h,1,2> orientations could result from a low Taylor value nucleation criterion.
Thermomechanical Treatment for Enhancing Deep Drawability of Copper-Bearing Bake Hardening Steel
Authors: Koo Yang Mo , Oh Kyu Hwan , Lee Dong Nyung
Published: January 2012

A two-step rolling-annealing process has been developed to increase the <111>//ND (γ fiber) component in the recrystallization texture of a copper-bearing bake hardening steel. The two step process comprises the first rolling by a low reduction in thickness and subsequent annealing at 780°C, followed by the second rolling by a high reduction and subsequent annealing at 780°C. The first rolling process aims at seeding the γ fiber oriented grains, so that they can grow at the expense of differently oriented grains developed in the second rolling process. In this way the density of γ fiber component in the recrystallization texture of the bake hardening steel much increases compared with that in the conventional one-step rolling-annealing process.
Evolution of Crystallographic Texture in Pure Iron and Commercial Steels by γ to α Transformation
Authors: Sung Jin Kyung , Lee Dong Nyung
Published: January 2012

A novel method has been discovered for controlling the crystallographic orientation of pure iron using the γ to α phase transformation. When pure iron with clean metal surfaces undergoes the γ to α phase transformation, it develops a strong cube-on-face texture ({100}<0vw>) with the grain size being larger than the sheet thickness. The mechanism controlling the <100> orientation obtained is associated with the fact that the {100} faces are elastically compliant so that the <100> texture can develop in a manner consistent with minimization of strain energy. However, in commercial steels, although so many texture analyses have been conducted, the cube-on-face texture has been rarely observed. According to thermodynamic analysis, surface oxidation in commercial steels appears to be responsible for the deterioration of the <100> texture. This phenomenon can be explained in terms of the modification of the inherent elastic anisotropy of metal surface by the surface oxidation.
Calculation Methods to Determine Crystallographic Elements Based on Electron Diffraction Orientation Measurements by SEM/EBSD or TEM
Authors: Zhang Yu Dong , Li Zong Bin , Esling Claude , Zhao Xiang , Zuo Liang
Published: January 2012

In the present work, we summarized two calculation methods to determine some specific crystallographic elements based on electron diffraction orientation measurements by SEM/EBSD or TEM. The first one is to determine the twin type and twinning elements of crystal twins based on the minimum shear criterion, using the experimentally determined twinning plane for Type I twin and compound twin or twinning direction for Type II twin as initial input. The method is valid for any crystal structure. The second one is one to determine the plane indices of the faceted interfaces where the orientation relationships (ORs) between the adjacent crystals are reproducible. The method requires one prepared sample surface instead of two perpendicular surfaces. These methods are expected to facilitate the related microstructural characterizations.
Effect of Intercritical Annealing Time on Microstructure and Mechanical Behavior of Advanced Medium Mn Steels
Authors: Arlazarov Artem , Gouné M. , Bouaziz O. , Hazotte A. , Kegel F.
Published: January 2012

The study about the influence of intercritical annealing time on a cold rolled 0.1%C – 4.6%Mn (wt.%) steel was performed. The tensile tests show an interesting balance between strength and ductility especially after 7 hours annealing at 670°C. A part of this good result can be explained by the presence of rather high fraction of metastable austenite at room temperature. On the other hand a very complex microstructure combining lath-like and polygonal features was observed making the interpretation complicated.
Dynamic Recrystallization Mechanisms Operating under Different Processing Conditions
Authors: Belyakov Andrey , Dudova Nadezhda , Tikhonova Marina , Sakai Taku , Tsuzaki Kaneaki , Kaibyshev Rustam
Published: January 2012

Dynamic recrystallization (DRX) is one of the most important mechanisms for microstructure evolution during deformation of various metals and alloys. So-called discontinuous DRX usually develops in structural materials with low to medium stacking fault energy during hot working. The local migration, i.e. bulging, of grain boundaries leads to the formation of recrystallization nuclei, which then grow out consuming work-hardened surroundings. The cyclic character of nucleation and growth of new grains during deformation results in a dynamically constant average grain size. The dynamic grain size is sensitively dependent on temperature and strain rate and can be expressed by a power law function of flow stress with a grain size exponent of about-0.7 under conditions of hot working. Recent studies on DRX phenomenon suggest that a decrease in deformation temperature changes the structural mechanism for new grain formation. As a result, the grain size exponent in the relationship between the dynamic grain size and flow stress approaches about-0.25 under warm working conditions.
Influence of Rolling Temperature and Cooling Rate on Microstructure and Properties of Pipeline Steel Grades
Authors: Carretero Olalla V. , Petrov Roumen H. , Thibaux Philippe , Liebeherr Martin , Gurla P. , Kestens Leo A.I.
Published: January 2012

Thermo-mechanical control processing (TMCP) is a powerful tool for development of high strength low alloy (HSLA) steels. The understanding of the effect of process parameters on the microstructure of these steels is a key aspect for the optimization of their mechanical properties. The influence of the rolling temperatures and the cooling conditions on the texture, strength and toughness of HSLA steel was investigated. Two stage controlled rolling (roughing and finishing) was carried out on a laboratory rolling mill. Four different compositions were rolled by maintaining same roughing conditions but varying the process parameters of the finish rolling, namely, start finish rolling temperature (SFRT), finish rolling and cooling temperatures. Subsequent to rolling, two different cooling routes were used, namely, air-cooling (AC) and accelerated water cooling (ACC). For the ACC route, the plates were subsequently heat treated to simulate coiling. The microstructure and texture obtained before and after each TMCP schedule were characterized quantifying the phases, grain size and texture by means of EBSD and XRD and associated with the mechanical properties. It was found that SFRT has a strong impact on both strength and toughness if the material was air-cooled. Plates rolled at lower temperature showed better strength and toughness than ones rolled at high temperature in both air-cooling and ACC due to grain refinement. However, for the material that was processed through ACC and coiling simulation, the strength increased without any substantial effect on the toughness. These results provide an interesting insight on the industrial processing of HSLA steels.
Thermo-Mechanical Processing of Low Manganese, Titanium Added Pipeline Steels
Authors: Dehghan-Manshadi Ali , Dippenaar Rian J.
Published: January 2012

Thermo-mechanical processing of a new family of low carbon, low manganese, titanium added steels was studied under a variety of simulated conditions. In this paper emphasis is placed on developing a better understanding of the effect of Ti and N on the microstructural development and mechanical properties of these new steel types. Also, the behavior of precipitates during hot deformation was examined. The results indicated that steel with a Ti/N ratio lower than the stoichiometric value provide best mechanical properties.
Modelling Deformation-Induced Precipitation Kinetics in Microalloyed Steels during Hot Rolling
Authors: Guo Zhan Li , Miodownik A.P.
Published: January 2012

This paper reports the framework of a computer model that calculates the precipitation kinetics of MX type carbides or carbonitrides from austenite matrix in microalloyed steels during hot rolling. The kinetic model is based on the classical Johnson-Mehl-Avrami theory adapted to include the saturation of nucleation sites. The effect of deformation on precipitation kinetics is quantitatively described through its effect on flow stress, from which the number of potential nucleation sites can be estimated. The time-temperature precipitation diagram can then be calculated for a given alloy chemistry and deformation conditions. A preliminary study has been carried out to test its performance in both undeformed and deformed conditions.
Effect of Quenching and Partitioning Temperatures in the Q-P Process on the Properties of AHSS with Various Amounts of Manganese and Silicon
Authors: Jirková Hana , Kučerová Ludmila , Mašek Bohuslav
Published: January 2012

The use of the combined influence of retained austenite and bainitic ferrite to improve strength and ductility has been known for many years from the treatment of multiphase steels. Recently, the very fine films of retained austenite along the martensitic laths have also become the centre of attention. This treatment is called the Q-P process (quenching and partitioning). In this experimental program the quenching temperature and the isothermal holding temperature for diffusion carbon distribution for three advanced high strength steels with carbon content of 0.43 % was examined. The alloying strategies have a different content of manganese and silicon, which leads to various martensite start and finish temperatures. The model treatment was carried out using a thermomechanical simulator. Tested regimes resulted in a tensile strength of over 2000MPa with a ductility of above 14 %. The increase of the partitioning temperature influenced the intensity of martensite tempering and caused the decrease of tensile strength by 400MPa down to 1600MPa and at the same time more than 10 % growth of ductility occurred, increasing it to more than 20%.
Evaluation of the Behaviour and Properties of a High-Si Steel Processed Using Direct Quenching and Partitioning
Authors: Somani Mahesh Chandra , Karjalainen L. Pentti , Porter David A. , Misra R.D.K.
Published: January 2012

An experimental steel containing in weight % 0.2C-2.0Mn-1.5Si-0.6Cr has been laboratory hot rolled, direct quenched into the Ms - Mf range and partitioning annealed in order to explore new possibilities for making 1100 MPa yield strength structural steels with better combinations of strength, ductility and impact toughness. Two austenite states prior to quenching were investigated: recrystallized and strained. Gleeble simulations were used to determine appropriate cooling rates and cooling stop temperatures for obtaining martensite fractions in the range 70-90%. Desired martensite - austenite microstructures were achieved, and ductility and impact toughness were better than those obtained via the simple direct quenching of a lower carbon steel in the same strength class.
Hardening of Al-Mg-Si Alloys and Effect of Particle Structure
Authors: Gulbrandsen-Dahl Sverre , Marioara Calin D. , Pedersen Ketill Olav , Marthinsen Knut
Published: January 2012

In the present study, several Al-Mg-Si alloys have been studied with respect to microstructure characteristics, i.e. particle statistics, and resulting mechanical properties. The alloys and tempers represents a wide range of type of hardening particles stretching from pre-β’’, via β’’, to post-β’’ particles such as β’, U1, U2 and B’, and various sizes, number densities and volume fractions of these particles. The correlation between volume fraction of hardening precipitates and mechanical strength is strong within alloys with pre-β’’ and β’’ as the main hardening precipitates, but this correlation does not fit for alloys with post-β’’ precipitates. However, a strong correlation between mechanical strength and both number density and cross-section area of the hardening precipitates is found, independent of type of precipitate. The consequences of these correlations are discussed with respect to proposed hardening models found in the literature.
Delamination of Cu and Ti Thin Films Deposited by Magnetron Sputtering on Cu Substrate: Analysis of Reasons
Authors: Egorov G. P. , Volkov A. A. , Golstcev V.U.
Published: January 2012

Multilayer thin-film structures are widely used in microelectronic, optoelectronic and micro-/nanoelectromechanical devices. Mechanical properties and mechanical stresses are very critical for such devices. Structural stresses are composed of an intrinsic part resulting from growth defects and a thermal part caused by the mismatch of the thermal expansion coefficients of the different materials in the multilayer system and between coating and substrate. Excessive tensile stresses result in cracking of the film and/or substrate, and compressive stress can cause buckling. Determination and control of stress is an important scientific issue for both functional thin films and engineering coatings from the viewpoint of performance and integrity. In the present study the in situ stress measurements for thin films of Ti (300nm thick) and Cu (1000nm thick) sputtered on Cu substrates were performed using a method proposed in [6]. The stresses that occurred in the Ti film were tensile, stresses that occurred in the Cu film were compressive. The continuous measurements were performed both during the process of the deposition and after the magnetron cut off. The film delamination from a substrate occurred in both cases. The analysis of obtained curves (the specific force versus time) was performed. Analysis revealed that the arising stresses are not caused by any nonstationary heating process of the material surface. Local buckling due to interatomic binding weakening can lead to Cu film delamination. The major cause of Ti film delamination can be a microcracking due to substrate’s thin surface layer yielding.
Fabrication and Characterisation of Diluted Magnetic Semiconductors Thin Films Using Ion Beams
Authors: Ionescu M. , Photongkam P. , Siegele R. , Deslantes A. , Li S. , Cohen D.D.
Published: January 2012

The intrinsic n-type (II-VI) semiconductor ZnO may become ferromagnetic at room temperature, by small additions of magnetic ions, resulting in what is called a Diluted Magnetic Semiconductors (DMS). The potential application of DMS in spintronic devices of is driving the research effort to dope magnetic elements into this semiconductors with a depth distribution as uniform as possible. The doping levels and the depth distribution of dopants are critical parameters for the magnetic properties of this material and the possible clustering of dopants can play a significant negative role in its macroscopic magnetic properties. Thin ZnO (0001) films of between 100nm and 500nm, grown on c-Al2O3 by MOCVD were implanted with Co, Eu and Co+Eu by ion irradiation at low energies. In order to improve the depth distribution of dopants, the ion implantation was carried out through a number of appropriately chosen range foils. The results show an increase in the level of dopant homogeneity throughout the entire thickness of the film, and a ferromagnetic behavior above room temperature for Zn0.96Co0.04O, Zn0.96Eu0.04O and Zn0.92Co0.04Eu0.04O.
Control of Grain Boundary Microstructures in Sputtered Gold Thin Films by Surface Energy-Driven Grain Growth
Authors: Kobayashi Shigeaki , Fukasawa Ryouta , Watanabe Tadao
Published: January 2012

The evolution of grain boundary microstructures in gold thin films during annealing was investigated in order to find a clue to the development of high performance thin films by grain boundary engineering. The {111} oriented grains with the lowest surface energy were preferentially grown by surface energy-driven grain growth during annealing. The sharp {111} texture was developed by annealing at the temperature more than 873K. The remarkably high fraction of low-Σ coincidence site lattice (CSL) boundaries occurred when the area fraction of {111} texture increased to more than 95%. In particular, the fraction of some low-Σ CSL boundaries (Σ1,Σ3,Σ7) for the most sharply {111} textured specimen was found to be one order higher than those predicted for a random polycrystal. The utility of grain boundary engineering is discussed for controlling the performance degradation caused by the percolation phenomena of grain boundary diffusion in gold thin films.
Modeling of Heat Treatment of Randomly Distributed Loads in Multi-Zone Continuous Furnaces
Authors: Hassan Alaa A. , Hamed Mohamed S.
Published: January 2012

A model for the heat treatment of randomly distributed metal parts processed in multi-zone continuous mesh-belt furnaces has been developed. The model accounts for the heat transfer by convection and radiation to the load and the belt. The effect of gas radiation due to the presence of CO2 and/or H2O gases in the furnace atmosphere has been accounted for. The effect of conduction, convection, and radiation within the parts has been considered. The effective thermal properties of the load have been calculated using a new model developed for randomly distributed parts. The effective thermal properties model has been developed using experimental data obtained from transient experiments carried out at the Thermal Processing Laboratory (TPL) of McMaster University. The continuous furnace model is capable of predicting temperature distribution within the load and the belt. It has been validated using real-life data obtained from test runs carried out at two heat treatment facilities in Ontario, Canada. The effects of load density, load emissivity and belt speed on furnace productivity have been investigated using the present continuous furnace model.
CdS Thin Film Growths on Sapphire Substrates Having Heteroepitaxial Transparent Conducting Underlayers
Authors: Sato Yuichi , Arai Manabu , Ito Kazuki
Published: January 2012

Cadmium sulfide (CdS) semiconductor thin films were grown on sapphire single-crystal substrates. Indium oxide (In2O3) and zinc oxide (ZnO), which are typical transparent conducting materials, were heteroepitaxially grown on sapphire substrates as underlayers before the cadmium-based semiconductor thin films were grown on them. Subsequently, cadmium-based thin films were heteroepitaxially grown on the transparent conducting under-layers. Crystallinity and photoluminescence properties of the cadmium-based thin films grown on the underlayers were evaluated and compared with those of the cadmium-based thin films grown directly on sapphire substrates.
Simplified Simulation of the Friction Stir Welding Process. Influence of the Boundary Conditions Modelling
Authors: Desrayaud Christophe
Published: January 2012

A simple three dimensional thermomechanical model for FSW is used in the present paper. It is developed from the model proposed by Heurtier [1] improved by Jacquin [10] to account for the eulerian cooling flux due to the tool motion during welding. The velocity fields used to describe the bulk flow around the tool are introduced in the particular derivative of the thermal equilibrium equation. The complete thermomechanical history of the material during the process can then be accessed by temperature and strain rate contours.
Thermoplastic Adhesive for Thermosetting Composites
Authors: Hou Meng
Published: January 2012

Technique of including a thermoplastic film as the outermost layer of thermoset composites have been developed as an attempt to join the thermoset composites using fusion bonding methods. Special thermoplastic in the form of film was incorporated onto the surface of thermoset composites during co-curing process. Semi-Interpenetration Polymer Network [s-IPN] was formed between thermoplastic and thermoset polymers. The thermoset composites can be fusion bonded using co-consolidation and localized heating through their incorporated thermoplastic surfaces. The mechanical properties of thermoset composites bonded with thermoplastic adhesive were equivalent or superior to the benchmark composites bonded with Cytec FM300K adhesive in terms of lap shear strength, high temperature, low temperature and anti-chemical resistance.
Optimization of Welding Parameters for Repairing NiAl Bronze Components
Authors: Li Hui Jun , Grudgings Daniel , Larkin Nathan , Norrish John , Callaghan Mark , Kuzmikova Lenka
Published: January 2012

The objective of this study is to determine an optimal welding procedure that can be implemented to repair damaged Nickel Aluminium Bronze (NAB) components. NAB is commonly used in marine applications where components are subject to a constant corrosive environment and high stresses. Research into ideal NAB microstructure for a marine application, was performed in order to gain a baseline for experimental analysis of potential welding procedures. The results indicated that the welding repair can be performed with a wide range of heat input. The effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties in the heat affected zone (HAZ) and weld metal was also investigated in this research. The dominant microstructure in weld metal at as-welded condition is coarse Widmanstatten type structure with high hardness; post-weld heat treatment resulted in significant grain refinement and hardness reduction in weld metal.