bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Nb Addition on Impact Toughness of As-Quenched Martensitic Stainless Steel for Automotive Applications
Authors: Mithieux Jean Denis , Godin Hélène , Gourgues-Lorenzon Anne Françoise , Parrens Coralie
Published: December 2018

This study presents how Nb addition allowed improving the Charpy impact toughness of a martensitic stainless steel by comparing a conventional AISI410 (12%Cr-0.1%C) and a 12%Cr-0.1%C-0.1%Nb steel after the same austenitization and quenching heat treatment. Adding niobium decreased the ductile-to-brittle transition temperature by 100°C with respect to the Nb-free steel. To identify quantitative fracture criteria for the two materials, the values of critical cleavage fracture stress were determined by the local approach to fracture, combining low temperature tensile tests on notched specimens and mechanical analysis by the finite element method. The main effects of niobium were to refine the grain size and to promote retained austenite films, resulting in a similar resistance to cleavage crack initiation but in a strong improvement of the ductile-to-brittle transition behavior by increasing the resistance to cleavage crack propagation.
Mechanical Performance of Titanium Alloys with Added Lightweight Interstitial Element for Biomedical Applications
Authors: Niinomi Mitsuo
Published: December 2018

Oxygen is considered to be an impurity in titanium and its alloys, and it enhances their brittleness. However, oxygen has also been recognized as a useful ingredient to improve the mechanical performance of titanium alloys for biomedical applications, because oxygen is a lightweight interstitial element that is non-toxic and non-allergenic. Some reports show that adding oxygen improves both the strength and the ductility of titanium alloys for biomedical applications. The effects of oxygen addition on the mechanical performance of titanium alloys for biomedical aplications are described.
The Improvement of Durability of Biodegradable Magnesium Alloy by Using Bio-Inspired Coating
Authors: Acquesta Annalisa , Carangelo Anna , Monetta Tullio
Published: December 2018

The observation of the natural world is increasingly inspiring the field of material science. A coating based on dopamine, the principle origin of the extraordinarily robust adhesion of the mussel to the solid surface, was used as an intermediate layer to decrease the degradation rate of a biodegradable device made of AZ31 magnesium alloy covered with an external organic coating. The dopamine-based film entailed a hydrophobic character to the sample, as confirmed by water contact angle test. The electrochemical analysis, made in Hank’s solution, showed that the bio-inspired film could improve the corrosion resistance of AZ31 when used together with an external organic coating.
Tissue Engineering Strategies to Promote Bone Repair
Authors: Collignon Anne Margaux , Rochefort Gaël Y.
Published: December 2018

Bone displays an amazing capacity for endogenous self-remodeling. However, compromised bone healing and recovering is on the ascent because of population aging, expanding rate of bone injury and the clinical requirement for the advancement of elective choices to autologous bone unions. Current strategies, including biomolecules, cell treatments, biomaterials and diverse combinations of these, are presently created to encourage the vascularization and the engraftment of the grafts, to reproduce at last a bone tissue with similar properties and attributes of the local bone. In this review, we look through the current techniques that are right now created, utilizing biomolecules, cells and biomaterials, to initiate, coordinate and potentiate bone regeneration and healing after damage and further talk about the natural procedures related with this repair.
Effect of Tempering on Hardness of Q&T Steel Plate
Authors: Goodall Aimee , Ju Yu Lin , Davis Claire , Strangwood Martin
Published: December 2018

Commercial production of high strength steel plates by the quenching and tempering (Q&T) route requires control of alloy design and heat treatment parameters to achieve the desired strength and toughness through thickness. Plates with different thicknesses (up to approximately 100 mm) are produced for applications in the energy and power or lifting and excavation sectors. For thick plate the difference in cooling rate through thickness affects the as-quenched microstructure with martensite, auto-tempered martensite and lower and/or upper bainite being present. The different as-quenched microstructures can show a different response to tempering which affects the final strength and toughness.In this study the starting microstructure of a low alloy 0.17 wt% C Q&T steel has been varied using isothermal heat treatment at 430 °C to create mixed martensite and lower bainite microstructures (nominally 25:75; 50:50 and 75:25 percentages). The effects of tempering at 600 °C for times between 0.5 and 16 hours on the carbide precipitates and hardness of the mixed microstructures have been investigated and compared to the tempering response of single phase (martensite and lower bainite) microstructures. It has been found that the hardness decrease due to tempering is larger in the martensitic structure than the bainitic structure due to more rapid carbide coarsening. The as-quenched hardness of the mixed microstructures can be predicted by a rule of mixtures using the single phase properties. The tempering response of the mixed microstructures is discussed.
Integration of Press-Hardening Technology into Processing of Advanced High Strength Steels
Authors: Jirková Hana , Opatová Kateřina , Káňa Josef , Bublíková Dagmar , Bystrianský Martin
Published: December 2018

Development of high strength or even ultra-high strength steels is mainly driven by the automotive industry which strives to reduce the weight of individual parts, fuel consumption, and CO2 emissions. Another important factor is the passenger safety which will improve by the use of these materials. In order to achieve the required mechanical properties, it is necessary to use suitable heat treatment in addition to an appropriate alloying strategy. The main problem of these treatments is the isothermal holding time. These holding times are technologically demanding which is why industry seeks new possibilities to integrate new processing methods directly into the production process. One option for making high-strength sheet metals is press-hardening which delivers high dimensional accuracy and a small spring-back effect. In order to test the use of AHSS steels for this technology, a material-technological modelling was chosen. Material-technological models based on data obtained directly from a real press-hardening process were examined on two experimental steels, CMnSi TRIP and 42SiCr. Variants with isothermal holding and continuous cooling profiles were tested. It was found that by integrating the Q&P process (quenching and partitioning) into press hardening, the 42SiCr steel can develop strengths of over 1800 MPa with a total elongation of about 10%. The CMnSi TRIP steel with lower carbon content and without chromium achieved a tensile strength of 1160 MPa with a total elongation of 10%.
Microstructural Evolution and Deformation Behavior of Cold-Rolled Fe-Mn-Al-C Low-Density Steel
Authors: Zhou Nai Peng , Song Ren Bo , Li Xuan , Niu Wen Jie
Published: December 2018

Low-density medium-manganese steels offer a vast development prospect for industrial application due to their outstanding combination of mechanical properties and density reduction. The microstructural evolution following tensile deformation of cold-rolled and annealed Fe-10Mn-10Al-0.7C steels was investigated by means of SEM and TEM microstructure analysis and XRD measurements. Annealing in the range of 700-1100 °C led to an austenite-ferrite dual-phase microstructure that was characterized by tensile strength of 700-1100 MPa and elongation of 6-34%. κ-carbides were observed in steels annealed at relatively low temperatures (700-850 °C). The steel exhibited the optimum combination of tensile strength of 930 MPa and elongation of 34% after annealing at 900 °C for 0.5 h. The stacking fault energy was estimated to be 69mJ/m2 considering the difference between average constituent and practical constituent of austenite caused by the high ferrite fraction. The deformed microstructures of the austenite exhibited the typical planer glide characteristics in sequence of dislocation array, Taylor lattice, Taylor lattice domain and microband. And the wavy glide occurs in ferrite was manifested by tangled dislocation and dislocation cells.
Effect of Precipitation State on Strength and Toughness of Precipitation Hardened Hot Rolled Steel Sheet
Authors: Yokoyama Takafumi , Taniguchi Shunsuke
Published: December 2018

In this work, to clarify the effect of carbide precipitation state on strength and toughness, Ti,V alloyed precipitation hardened ferrite single phase steel sheets with different carbide size were investigated. In order to change the precipitated particle size, cooling conditions after hot rolling were changed. Under condition A, steel sheets were cooled to 873K by water spray (for fine precipitation). Under condition B, steel sheets were air-cooled from 1053K for 20sec, then cooled by water spray to 873K (for coarse precipitation). The experimental results were following. The balance of tensile strength and Charpy absorbed energy was better in condition B. (Ti,V)C were observed in both conditions, but the size of (Ti,V)C were larger in condition B. From the above, it was suggested that as the carbide size become larger, the decrease in toughness per strengthening amount becomes smaller.
Creep Property of Boron Added 9Cr Heat Resistant Steels after Welding
Authors: Matsunaga Tetsuya , Souissi Maaouia , Sahara Ryoji , Hongo Hiromichi , Tabuchi Masaaki , Zhang Wei , Mills Michael J.
Published: December 2018

Although welding results in premature failure by type IV fracture under high temperature creep conditions, the alloy design of light elements such as boron addition and nitrogen reduction enhances the creep lifetime of 9Cr heat resistant steel. In particular, the simulated heat affected zone (SHAZ) sample of new 9Cr steel (called TA steel) shows about 10 times longer creep lifetime than that of the standard Gr. 91 steel. The welded TA steel is thus expected to exhibit good creep properties because its SHAZ sample has coarser grains and suppresses type IV fracture. The preservation of base metal’s microstructure after welding results from the precipitate morphology, such as high grain boundary coverage by precipitates and low amount of MX being nucleation sites of ferrite grains during the a-g phase transformation. In addition, the increase of stability of M23C6 affects high pinning pressure toward grain boundary migration upon rapid heating during welding. First-principles calculations confirm the increased stability when boron is absorbed by M23C6. Moreover, the calculations reveals that boron decreases the coherency between matrix and M23C6, suppressing grain coarsening during creep tests in TA steel. It is concluded that the increased microstructural stability during welding and long high temperature exposure generates the elongated creep lifetime in welded TA steel including about 0.01 wt% boron and less than 0.01 wt% nitrogen.
Processing and Mechanical Properties of Highly Formable Ferritic High Strength Steel Containing Titanium Nanocarbides for Automotive Applications
Authors: Lange Alexander , Abraham Sarah , Fechte-Heinen Rainer , Winzer Nicholas , Kern Andreas
Published: December 2018

The recently developed CH-W® 800 hot-rolled steel is specifically developed for automotive chassis applications that require both high strength and outstanding formability. A completely ferritic microstructure allows hole expansion ratios of 90% and more, which indicates the remarkable formability of the material. The tensile strength of at least 800 MPa is mainly due to its very fine-grained microstructure as well as titanium carbide nanoprecipitates.
Microstructures and Properties of DP 600 Steel Conventionally Treated and Intercritically Annealed from As-Quenched Martensite
Authors: Centeno Dany Michell Andrade , Goldenstein Hélio
Published: December 2018

In this work a DP 600 Dual Phase steel, conventionally treated in order to obtain 40 to 60% austenite at the intercritical temperatures, called reference sample, was compared to samples from the same steel, initially fully austenitized and quenched to 100% martensitic structure and subsequently intercritically tempered once (one step) or twice, (two steps) at intercritical temperatures so as to obtain the same volume fractions of austenite as the conventional DP steel. The single step heat treatment is QL, quench and lamellarization; the two step heat treatment is called QLT, quench and lamellarization and tempering. Heat treatments were conducted on a quenching dilatometer. Samples were characterized by optical, SEM-FEG, EBSD imagining and X Ray Diffraction. Mechanical properties were evaluated by microhardness and tensile tests on sub-size specimens. The results show that QL samples present a complex microstructure composed of ferrite (carbide free high temperature tempered martensite) and fresh martensite composed of crystallites of the order of 1 to 5 μm, with volume fractions of ferrite and martensite similar to the reference samples. X-ray diffraction showed the presence of retained austenite in all treatment conditions, larger for the reference samples when compared with the QL; EBSD images show the retained austenite finely dispersed between the martensite laths and within the limits of martensite blocks. The tensile strength of the QL has higher values than reference DP 600 steel for the similar martensite volume, with smaller uniform and total elongations.
Microstructures and Mechanical Properties of Tough Ductile Ultrahigh-Strength Steels Processed through Direct Quenching and Partitioning
Authors: Kantanen Pekka K. , Somani Mahesh Chandra , Porter David A. , Kömi Jukka I. , Misra Devesh K.
Published: December 2018

Using a novel TMR-DQP processing route, two ultrahigh-strength steels have been developed with yield strengths up to 1100 MPa combined with good uniform and total elongations and low-temperature impact toughness. Processing involved thermomechanically controlled rolling including significant reductions below the recrystallization stop temperature (RST), subsequent direct quenching to desired quench stop temperatures between Ms and Mf and finally partitioning of carbon from the supersaturated martensite to the untransformed austenite in a furnace at the quench stop temperature. Samples were cooled slowly in the furnace over 50 hours to simulate the cooling of coiled strips on industrial hot strip mills. The approach used was to utilize a suitable 0.3C steel composition based on high silicon and/or aluminium contents. Detailed metallographic studies using LOM, FESEM-EBSD, TEM and XRD showed that the desired martensite-austenite microstructures were achieved. The advantage of strained austenite in respect of refinement of martensite packets/blocks was clearly evident. Austenite was finely divided between martensite laths and only an insignificant amount of austenite existed as pools. The fine lath martensite structure with narrow interlath retained austenite films enabled the achievement of excellent combinations of mechanical properties. Promising results in respect of microstructures and mechanical properties indicate that there are possibilities for developing tough ductile structural and abrasion-resistant steels through the TMR-DQP route.
Microstructure Characterization of Quenching and Partitioning Steels
Authors: de Diego Calderon Irene , Salib Matthieu , Kabou Nora , Arlazarov Artem
Published: December 2018

A steel containing Fe-0.2C-2Mn-Si-Al was annealed using intercritical Q&P cycles. Quenching temperature and partitioning time at 440°C was varied. Analysis of microstructure evolution during such Q&P treatments was performed using different characterization tools: FEG-SEM, EBSD, dilatometer and saturation magnetization measurements. Especially, phenomena taking place during partitioning were investigated. The microstructure was analyzed at the end of soaking, before and after partitioning and at the end of the annealing cycle. It was found that bainite transformation happens during partitioning and has a significant effect on the final retained austenite fraction. Quenching temperature has an important effect on both martensitic transformation during cooling and subsequent bainite transformation during partitioning.
Effect of Gas Tungsten Arc Welding Condition on Hydrogen Absorption in a Duplex Stainless Steel
Authors: Mirzaei Bahram , Itoh Goroh , Khodabandeh Alireza
Published: December 2018

The use of duplex stainless steels (DSSs) is steadily increasing. For many uses where joining is needed, gas tungsten arc welding (GTAW) is one of the most important joining methods for DSSs. Since hydrogen embrittlement (HE) occasionally occurs in DSSs, understanding the relationship between the extent of HE and the welding condition is crucial to prevent HE. In this research, the effect of the heat input of GTAW process on the microstructure and the extent of HE in a UNS S31260 (JIS SUS329J4L) has been investigated. For this purpose, three samples have been prepared with diffrent velosity. All the samples have been cathodically hydrogen-charged, and then subjected to tensile test at a strain rate followed by fractography observation. Thermal desorption spectroscopy (TDS) has been carried out on the samples welded at low and average velosities. The results showed that tensile properties of the welded specimens were lower than those of base metal due to coarsening of the matrix ferrite grains and loss in the fraction balance of ferrite and austenite phases in the weld metal zone, where fracture took place.
3rd Generation AHSS : Mechanistic Responses Enabling Cold Deformation during Stamping
Authors: Branagan Daniel James , Parsons Craig S. , Machrowicz Tad V. , Frerichs Andy E. , Meacham Brian E. , Cheng Sheng , Sergueeva Alla V.
Published: December 2018

Due to increasingly stringent regulations governing fuel economy and emissions, new technological developments towards automobile efficiency are in play including lightweighting by reducing weight of the structural components. The historical development of steel grades for autos has resulted in strength increases, including in recent advanced high strength steels (AHSS), but it has come with commensurate decreases in ductility and formability. NanoSteel 3rd Generation AHSS overcomes the trade-off in ductility due to novel structural changes during cold deformation through a complex Nanophase Refinement and Strengthening (NR&S) mechanism leading to material strengthening. During stamping, the ability of a steel blank to be formed into complex parts is paramount and it has to retain sufficient ductility for energy absorption during a subsequent crash event. In this paper, the specific characteristics of the NR&S mechanism in two NanoSteel grades will be detailed including structure and property changes during stamping analyzed by utilizing destructive and non-destructive approaches to predict localized yield strength changes in the final stampings.
Strengthening Mechanisms in Low Carbon Lath Martensite as Influenced by Austenite Conditioning
Authors: Kennett S.C. , Krauss George , Findley Kip O.
Published: December 2018

Low carbon lath martensitic microstructures are used in various steel products requiring high strength and toughness. These microstructures are conventionally produced through re-austenitizing and quenching followed by low or high temperature tempering. It is also possible to produce lath martensite through direct quenching immediately following thermomechanical processing. In this study, deformation below the austenite recrystallization temperature before quenching to form martensite was simulated through laboratory scale Gleeble processing of a 0.2 weight percent carbon ASTM A514 steel microalloyed with up to 0.21 weight percent niobium. Thermomechanical processing generally increases the dislocation density of the as-quenched martensite, which is sensitive to the austenite grain size before thermomechanical processing. The hardness of the thermomechanically-processed steels is generally greater than steels austenitized at comparable temperatures without deformation; this hardness difference is attributed to the increase in dislocation density and increased lath misorientation in the thermomechanically-processed conditions. The hardness is generally independent of prior austenite grain size for the thermomechanically processed conditions in contrast to conventionally austenitized and quenched conditions, which have a Hall-Petch correlation with austenite grain size. The strength increase of the thermomechanically processed conditions compared to the conventionally austenitized and quenched conditions is maintained after tempering. However, there is a larger drop in strength for small prior austenite grain sizes for both conventionally austenitized and quenched and thermomechanically processed steels. Overall, the strength of these lath martensitic steels can be directly related to dislocation density through a Taylor hardening model.
Behavior of Fatigue Cracks Generated from a Small Artificial-Defect in Plain Specimen of Copper Processed by Equal Channel Angular Pressing
Authors: Goto Masahiro , Iwamura Takashi , Yamamoto Takaei , Han S.Z. , Kitamura Junichi , Yakushiji Terutoshi
Published: December 2018

Fatigue tests of ultrafine-grained copper processed by equal channel angular pressing were conducted on the round-bar specimens with a small artificial-defect. The fatigue crack initiated from the defect at an early fatigue stage. After the crack initiation, the crack grew with a 45° inclination to the loading axis at stress amplitudes above 180 MPa. At the stress less than 160 MPa, however, the crack grew perpendicular to the loading axis. The physical background of deferent crack path directions between high-and low-stresses was discussed from the viewpoint of a morphological feature of damaged traces along the crack path.
Experimental Analysis about Heat Treatment Distortion in Bearing Race
Authors: Hidaka Hideyuki , Miyamoto Yuji , Matoba Riichiro
Published: December 2018

It’s well known that the vehicle fuel economy is improved by reducing the weight of their structural and mechanical components. Therefore, there is a demand of bearing race with thin thickness for weight reduction. But, this thickness reduction also causes a large oval distortion in bearings after Heat Treatment (HT). The factors affecting the HT distortion are extremely complicated, which makes it difficult to do rectification only by experimental analysis. There is also a limitation in numerical analysis due to the lack of workable model for HT distortion. Therefore, the aim of this study is to identify the effective factors of HT distortion by experimental approach in order to build suitable numerical simulation model that can estimate HT distortion. The material used in this study is a conventional case-hardened steel (Fe-0.4mass%C-Cr-Mn). The ring with the diameter of 100mm is heat treated and quenched. The resulting HT distortion is evaluated by measurement of maximum and minimum diameter of the race. A jig was developed to correct the ring shape during heat treatment, which helped in identifying that the quenching affects more than 50% of HT distortion. From these results, we developed a cooling equipment to reproduce inhomogeneous cooling rate by controlling oil flow toward the exterior of the ring. The quenching with this equipment reveals that inhomogeneous flow with opposite side (0 degree and 180 degree) reproduces a large oval distortion. The data obtained from the experimental analysis is suitable for developing the numerical model for HT distortion.
Cast Iron Metalworks in European Urban Furniture Dating Back to the 19th and the Early 20th Centuries
Authors: de Ruggiero Alba Clara , Calzolari Laura , Soffritti Chiara , Varone Alessandra , Garagnani Gian Luca
Published: December 2018

The term “street furniture” includes numerous elements (e.g. street lamps, benches, fountains, gazebos) easing city life, complementing architecture and contributing to decorate urban areas. Despite the massive presence of street furniture in the urban environment, the knowledge about its evolution through the centuries is frequently ignored or neglected. This study analyses the main metallurgical features of twenty cast iron metalworks dating back to the 19th and early 20th centuries manufactured in cast iron foundries mainly located in Italy, France and England. The experimental activity was carried out in collaboration with “Fondazione Neri – Museo Italiano della Ghisa” (Longiano, FC, Italy).The microstructure was determined by means of optical microscopy (OM), whereas the semi-quantitative chemical composition was evaluated through scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS).The experimental results highlight the lack of a shared metallurgical culture in steel industry over the last one hundred and fifty years, since non-uniform microstructural features were observed among the specimens produced in that period in the geographical areas under study.
Influence of Cu Addition on Microstructure and Mechanical Properties of Fe-0.08C-1Mn-2.5Ni Steel
Authors: Xi Xiao Hui , Chen Li Qing , Zhao Yang , Wang Zhao Dong
Published: December 2018

In addition to precipitation strengthening effect as Cu precipitates in steel, Cu-containing steel is generally believed to have ability to resist corrosion. However, there are some issues, e.g. strengthening mechanism and appropriate copper content, remaining to be clarified. In this presentation, an offshore platform steel Fe-0.08C-1Mn-2.5Ni was used as experimental materials and the emphasis was put on the comparative study of Cu-addition in terms of microstructural evolution and mechanical properties by using microstructural characterization and mechanical properties measurement. The continuous cooling transformation behavior of the two Cu-containing steels with varying contents was first compared. The Cu-containing precipitates were then determined by transmission electron microscopy (TEM) in the hot rolled steel plate after quenching and tempering. Finally, the effect of Cu-addition on precipitation strengthening and low temperature toughness was discussed considering the interaction of Cu precipitates with dislocation and martensite microstructure.
Titanium Alloys Anodic Oxidation: Effect of Experimental Parameters on Surface Colouring
Authors: Napoli Giuseppe , Zitelli Chiara , Corapi Domenico , Di Schino Andrea
Published: December 2018

The present study is focused on analysing the change of colours of anodized titanium and effects of applied electrolytic voltages on chromatics. The titanium specimens were anodized in 20 g/L citric acid and 20 g/L baking soda electrolyte by use of different voltages. The colours of anodized titanium were measured with a spectrophotometer and then evaluated in the CIELAB colour space. It is found that different volt produces different colours. Anodizing in the range of 15 V to 150 V produces respectively a wide spectrum of colour ranging from brown to fuchsia. It can be concluded that the colours of the anodized titanium are dependent upon the applied voltages.
Elemental Segregation and O-Phase Formation in a Gamma-TiAl Alloy
Authors: Gabrisch Heike , Krekeler Tobias , Lorenz Uwe , Rackel Marcus Willi , Ritter Martin , Pyczak Florian , Stark Andreas
Published: December 2018

Titanium aluminides based on the L10 ordered g-phase are promising structural light-weight materials for applications in aircraft engines. Typical compositions for γ-TiAl alloys lie in the range Ti-(44-48)Al (at.-%). For high creep resistance, a two-phase microstructure based on lamellar (α2+γ)-colonies is desirable that may be tuned towards better ductility by introducing pure γ-grains (near lamellar or duplex microstructure).γ-TiAl alloys are often alloyed with niobium for increased oxidation resistance and improved mechanical properties. HEXRD and TEM studies of the alloy Ti-42Al-8.5Nb revealed that the orthorhombic O-phase forms during annealing at 500-650°C. This orthorhombic phase has been known in Nb-rich, Al-lean, α2-based Ti-aluminides since the late 1980ies (Nb> 12.5 at.-%, Al< 31 at.-%) but the finding in γ-based alloys is new.TEM imaging showed that the O-phase is located within α2 lamellae of lamellar (α2+γ)-colonies. O-phase domains and α2 phase form small columnar crystallites based in the α2/γ interface. The columnar crystallites grow parallel to the [0001] direction of the α2 phase and appear as facets when observed along this direction. The evolution of domains and facets with annealing time and the chemical homogeneity of the phases are investigated.The results of STEM imaging show that O-phase domains form during annealing at 550 °C for 8hours or 168 hours. After 168 hours of annealing Nb segregations are observed by EDX mapping within O-phase domains. In comparison, no segregation of niobium is detected after 8 hours of annealing.
Effect of α2 Precipitation on Creep and Tensile Properties of Ga-Added Near-α Titanium Alloys
Authors: Kitashima Tomonori , Hagiwara Masuo , Ito Tsutomu , Hayakawa Masao , Iwasaki Satoshi
Published: December 2018

The effect of α2 precipitation on the creep and tensile properties was investigated for bimodal and lamellar microstructures in two Ga-added near-α Ti alloys with Al equivalences of 10.6 and 11.5. Fine α2 phase formed in the α phase of both alloys. The volume fraction of the α2 phase for the Al equivalences of 10.6 and 11.5 is equivalent to 57.6 % and 73.3 %, respectively, in the binary Ti-Al system at 600 °C. Creep tests were carried out under a constant stress of 310 MPa at 600 °C and tensile tests were performed at room temperature. Lamellar microstructure showed lower minimum creep strain rates than bimodal microstructure for both alloys. The increase in Al equivalence increased creep life by a factor of 1.6 and decreased the minimum creep strain rate from 6.51 × 10-8 s-1 to 3.99 × 10-8 s-1 in bimodal microstructure. In addition, the increase in Al equivalence decreased room temperature tensile elongation although both alloys contained a similar volume fraction of equiaxed α in a bimodal microstructure.
Microstructural Comparison of an Al-8.0Zn-1.8Mg-2.0Cu Alloy with Typical T6 and T76 Tempers
Authors: Xiong Bai Qing , Wen Kai , Zhang Yong An , Li Zhi Hui , Li Xi Wu , Huang Shu Hui , Yan Li Zhen , Yan Hong Wei , Liu Hong Wei
Published: December 2018

In order to analyze aging behavior of an Al-8.0Zn-1.8Mg-2.0Cu alloy, the microstructure of the alloy subjected to T6 and T76 states are investigated by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). Based on the precipitate observations, precipitate size distributions and average precipitate size are extracted from bright-field TEM images projected along 〈110〉Al orientation with the aid of an imaging analysis. The results indicate that the main precipitates are GPI zone, GPII zone and η' phase in the T6 alloy while η' phase and η phase in the T76 alloy. The bright-field TEM observations reveal that the matrix precipitates for the T6 alloy have small size and dispersive distribution while that for the T76 alloy has big size and sparse distribution. Both have discontinuously distributed grain boundary precipitates. Quantitative structural information including precipitate size distribution and average precipitate size has been calculated by an image analysis based on the bright-field TEM images projected along 〈110〉Al orientation. The results show that the T6 alloy has a narrower precipitate size range than the T76 alloy and thus the T6 alloy possesses a smaller average precipitate size than the T76 alloy.
Degradation of Hardness of Alloys from Phase Coarsening
Authors: Li Ji Cheng , Wang Ke Gang
Published: December 2018

The hardness of alloys after phase coarsening is analyzed through the linkage between the multiparticle diffusion simulation and the finite element method simulation. Our analysis demonstrates that considerable degradation of the hardness of alloys occurs due to phase coarsening, which is related to the precipitate sizes and their distribution within the alloy. The microstructural evolution alters the manners of the nucleation, multiplication and movement of dislocations within the material, and further leads to different degradation of macroscopic hardness of alloys.
Formation of Secondary Phases in the Boundary between Surface Defect Grains and Matrix in Third Generation Nickel-Based Single Crystal Superalloy Turbine Blades
Authors: Park Kee Hyun , Withey Paul
Published: December 2018

Ni-based single crystal superalloy turbine blades have excellent mechanical strength and resistance to corrosion and oxidation due to a uniformly distributed gamma prime phase in a gamma matrix. However, defect grains have been often found on the surface of turbine blades after manufacturing, which can be potential sites of crack initiation. In this study, several different types of surface defect grains formed in third generation Ni-based single crystal turbine blades, such as stray grains, freckle chain grains, equiax grains, and a new grain formed in surface scale, had been investigated. The grain boundary regions were observed by high resolution electron microscopy. Although the formation mechanism of each grain defect is different, secondary phases, such as rhenium-rich particles, have been always found in each grain boundary. In addition, depending on the existence of the secondary phases as well as the size of defect grains, different microstructures were observed even in the same defect grain boundary. Finally, the observed results suggest that if there is any boundary region in a turbine blade, secondary phases, such as Re-rich particles, can be found.
Forging Process Design and Simulation Optimization of a Complex-Shaped Aluminium Alloy Component
Authors: Chen Yan , Wang Song Wei , Song Hong Wu , Zhang Shi Hong
Published: December 2018

In order to meet the requirements of lightweight and replace steel with the aluminum for a component on the high speed rail, the forging process of a complex-shaped aluminum alloy component was researched and the parameters were optimized with the DEFORM-3D finite element simulation technology. The qualified products were finally obtained instead of the original steel castings by reducing weight of 65%. It is noted that the parts with complicated shape and non-symmetry, metal flow uneven during forging process that lead to incomplete forming, higher forging pressure problems. In this paper, such problems were analyzed couple with numerical simulation method based on a certain forming pressure. Moreover, the model and slot was reasonably designed. In addition, the size of blank was constantly optimized to change the metal flows direction and cavity filling mode. Finally, the forgings with good surface quality and mechanical properties were obtained by production test, and can be used as reference for this kind of forging components.
Investigation and Constitutive Modelling of High Strength 6xxx Series Aluminium Alloy: Precipitation Hardening Responses to FAST (Fast Light Alloys Stamping Technology) and Artificial Ageing
Authors: Zhang Qun Li , Dhawan Saksham , Luan Xi , Du Qiang , Liu Jun , Wang Li Liang
Published: December 2018

FAST (Fast light Alloys Stamping Technology) has recently been developed to efficiently and economically manufacture lightweight, high strength structural components from aluminium alloys sheet. Post-form strength prediction of 6xxx series aluminium alloy (AA6xxx) after FAST and multiple stage heat treatments has been a challenge. This is due to the effect of pre-existing dislocations induced via high temperature plastic deformation in the forming process. In the present research, a new PFS (post-form strength) model has been proposed to predict the age-hardening response of AA6xxx alloys undergoing FAST and subsequent thermal cycles. The model incorporates two sub-models, for simulating viscoplastic flow and predicting strength evolution respectively. The first sub-model incorporates a set of constitutive equations, developed to model the stress-strain curve of AA6xxx during FAST. The second sub-model employs precipitation-hardening and dislocation-hardening theories to simulate the evolution of microstructure and, as a consequence, strength of alloys undergoing artificial ageing cycles. This is calculated by considering the intrinsic resistance of the alloy to dislocation movement due to solute atoms and precipitates. The strength was computed accurately via the internal state variables method, in which dislocation density, volume fraction of precipitates, solute concentration and radii of precipitates were correlated. Furthermore, the model was validated by comparing results with transmission electron microscope (TEM) images as well as hardness measurements. Hence, the model performs as a powerful and comprehensive tool to simulate post-form strength of 6xxx series aluminium alloys that undergo complicated thermomechanical processes including high temperature deformation and post-form heat treatment, with less than 5% deviation between measured and predicted values.
Twinning and Detwinning Mechanisms in Beta-Ti Alloys
Authors: Gutierrez-Urrutia Ivan , Li Cheng Lin , Ji Xin , Emura Satoshi , Tsuchiya Koichi
Published: December 2018

We have investigated {332}<113> twinning and detwinning mechanisms in β-Ti alloys. Microstructure-twinning relations were evaluated in a β-Ti-15Mo (wt.%) alloy by statistical analysis of the evolving twin structure upon deformation by in-situ SEM testing and electron backscattering diffraction (EBSD). We find that most of the primary twins (~80%) correspond to the higher stressed variant and follow Schmid’s law with respect to the macroscopic stress. Detwinning mechanism was evaluated in a multilayered β-Ti-10Mo-xFe (x: 1-3 wt.%) by EBSD. We find that the detwinning process consists of two independent events that occur at two different microstructural regions, i.e. twin tips located at grain interiors and grain boundaries. Both detwinning modes can be explained from a thermodynamic standpoint where the boundary dissociation processes minimize the boundary free energy.
Microstructures of Ternary Eutectic Refractory Me-Si-B (Me = Mo, V) Alloy Systems
Authors: Hasemann Georg , Krüger Manja , Palm Martin , Stein Frank
Published: December 2018

The present work addresses the microstructure evolution of refractory Me-Si-B (Me = Mo, V) alloys consisting of a refractory metal solid solution phase (MeSS) and two intermetallic phases Me5SiB2 and Me3Si. The aim of the present study is to find the ternary eutectic composition in such systems which are expected to combine a well-defined eutectic microstructure with properties such as high strength, an excellent creep resistance at high temperatures and acceptable oxidation behavior. Two refractory metal systems based on molybdenum and vanadium are investigated. Various alloy compositions located in different primary solidification areas were produced by arc-melting and analyzed via SEM. The obtained results are discussed in the light of published liquidus projections. By carrying out these experiments, a MeSS-Me5SiB2-Me3Si ternary eutectic could be determined in both Me-Si-B systems.
Through-Scale Analysis of Strain Path Effects in Microalloyed Austenite Subjected to Reverse Rolling
Authors: Muszka Krzysztof , Majta Janusz , Gliwinski Marcin
Published: December 2018

Thermomechanical hot rolling processes are often realized using reverse rolling stands, where the rolled stock is fed forward and backward through the rolling gap. During those processes, material undergoes several strain reversals that significantly alter microstructure evolution of austenite with respect to continuously rolled counterparts. In Nb-microalloyed steels, where precipitation hardening is usually expected, the effects of strain reversal are especially complex. When rolling direction is reversed, both static recrystallization (SRX) kinetics and strain-induced precipitation (SIP) processes are slowed down due to decreasing dislocation density. It affects the competition between driving force for SRX and pinning pressure for SIP and, in turn, changes the non-recrystallization temperature (Tnr), compared to the case where strain path is linear. In the present paper, detailed through-scale analysis of strain path effects in microalloyed austenite will be presented. Physical simulation and detailed microstructural analysis will be employed to study global and local effects in microalloyed austenite after complex deformation histories. Conclusions regarding the influence of strain path changes on the interactions between SRX and SIP will be drawn.
Effect of Different Shot Peening Treatments on Fatigue Life in Ti Alloy
Authors: Harada Yasunori , Saeki Yuto , Takahashi Katsuhiko
Published: December 2018

The effects of peening conditions on the surface characteristics and fatigue life of titanium alloy was investigated using microshot peening, ultrasonic shot peening, and multiple shot peening. The use of microshot peening technology with minute media has become more widespread in consideration of the reduction of the notch effect in the material surface. The ultrasonic shot peening that uses media of several millimeters in size with ultrasonic vibration has attracted attention as a means to reduce the surface roughness. In the present study, an air-type and an ultrasonic type machine were used. In the microshot peening process, the media used was high-carbon cast steel and the hard powder, with an average diameter of 0.1 mm. The workpiece was commercial titanium alloy Ti-6Al-4V. In the microshot peening (MSP), work hardening was evident to the depth of approximately 0.3 mm from the surface. This depth was approximately three times the diameter of the media. However, the influence of the peening time on the hardness distribution was not great. In the ultrasonic shot peening (USP), work hardening was deeper in the material. This is because the diameter of the media used for ultrasonic machining was large. On the other hand, in the combined shot peening (CSP), a degree of hardness was higher at the top surface. However, the hardness patterns and values were pretty much identical to ultrasonic shot peening. The fatigue limit was thought to be greater in the microshot peening experiment because the work-hardened layer was formed near the workpiece surface.
Effect of One-Step and Two-Step Aging Treatments on Microstructure and Properties of an Al-9.0Zn-2.0Mg-2.0Cu Alloy
Authors: Wen Kai , Xiong Bai Qing , Zhang Yong An , Li Zhi Hui , Li Xi Wu , Huang Shu Hui , Yan Li Zhen , Yan Hong Wei , Liu Hong Wei
Published: December 2018

Aging treatments of an Al-9.0Zn-2.0Mg-2.0Cu alloy, which belongs to high strength aluminum alloy widely used in aerospace industry, are investigated by various techniques, including hardness, electrical conductivity, mechanical properties, transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The result shows that hardness and conductivity for one-step aging treatment increase with aging time prolongs while those for two-step aging treatment exhibit increment and decrement, respectively. Besides, the ultimate tensile strength (UTS) and yield strength (YS) for one-step and two-step aging treatments show slow increase and obvious decrease, respectively. Based on these, typical T6 and T76 aging regimes are extracted for microstructure observation. The matrix precipitates for the T6 alloy have small size and dispersive distribution while that for the T76 alloy has big size and sparse distribution. The grain boundary precipitates for both exhibit discontinuous distribution and the T76 alloy has larger size and broader precipitate free zones. The selected area diffraction patterns and HREM observations reveal that main precipitates for the T6 alloy are GPI zone, GPII zone and η' phase while for the T76 alloy are η' phase and η phase.
Effect of Alloy Composition and Pre-Ageing on the Stretch Formability of 6xxx Automotive Sheet Alloys
Authors: Zhong Hao , Cao Ling Fei
Published: December 2018

In this study, the effect of Mg/Si ratio, Cu content and/or pre-ageing treatment (e.g. 100 °C for 2 h and/or 200 °C for 20 s) on the stretch formability of 6xxx alloys was investigated through their influence on the work hardening and strain-rate hardening behaviour using tensile testing and forming limit diagram tests. The results showed that a high Mg/Si ratio, a low Cu content and/or the employment of pre-ageing could deteriorate the stretch formability due to the decrease in work hardening and/or strain rate hardening capabilities. Moreover, the stretch formability was observed to have an opposite correlation with the paint-bake response of the alloys studied.
Connecting the Microstructure Stability of Ni Based Superalloys to their Chemical Compositions
Authors: Yu Hao , Xu Wei , van der Zwaag Sybrand
Published: December 2018

The degradation of creep resistance in Nickel-based single crystal superalloys is essentially ascribed to their microstructure evolution. Yet there is a lack of work that manages to simulate the effect of alloying element concentrations on microstructure degradation. In this research, a computational model is developed to connect the rafting kinetics of Ni superalloys with their chemical composition, by combining thermodynamics calculation and an energy-based microstructure model. The isotropic coarsening rate and γ/γ misfit stresses have been selected as composition related parameter, and the effect of service temperature, time and applied stress are also taken into consideration to simulate the evolutions of microstructure parameters during creep process. The different generations of commercial Ni superalloys are selected and their chemical compositions are calculated based on this model. The simulated microstructure parameters are validated by the results from experimental results and the existing analytical model. The capability of the model in predicting the microstructure characteristics may provide instructional thought in developing a novel computational guided design approach in Ni superalloys.
The Double-sided Intrusion Spring
Authors: Celebi Fatih
Published: December 2018

In deep bite cases, proper planning and practice are important in achieving the successful treatment outcomes. Bite opening is obtained with the aid of incisor intrusion, molar extrusion, or a combination of them. Pure incisor intrusion is a challenge for clinicians because incisor intrusion mechanics generally cause molar extrusion or incisor flaring. In the present article, a new technique that can be used for incisor intrusion without the mentioned handicaps was introduced.