Brevet FR3099771A1 — publié le 20210212

Description Titre de l'invention : Full dense parts obtained by pressing hybrid titanium alloy powder by high velocity compaction and sintering in high vacuum [00ol] The present invention descrihes the process to achieve full theoretical density by pressing by high velocity compaction hybrid titanium powder without using any internai organic luhricant and sintering in high vacuum. [0002] Hybrid powdcr is dcnoted here as a mixture of spherical powder and dendritic powder or coral like morphology. [0003] The spherical powder of titanium is issued by gas atomizing process, GA, by the plasma rotating electrode process, PREP, or by plasma atomization, PA. [0004] The dendritic powder is issued from the Armstrong Process® (1). [0005] Titanium parts for aerospace and automotive applications represent a special interest because of their weight, excellent behavior in corrosive environment and good mechanical properties. [0006] In terms of technological aspects, the fabrication of titanium alloys by melting technology to produce ingots needs very good know how in order to obtain homogenous and high-quality ingots for conversion to mill products. Or, in practice, defects such as high interstitiel defects, solute segregation, high density inclusions, beta flecks or voids which occurs during solidification cannot be avoided. The difficulty to control the solidification depends as well on the chemical composition of the alloy. The high reactivity of titanium conduct to formation of interstitial defects such as high concentration of oxygen, carbon or nitrogen. As well, the high-density inclusions occur by contamination of titanium alloy with raw material (molybdenum, tantalum, tungsten or tungsten carbides) used in the production of the alloy (2). Therefore, the presence of TiN in the microstructure decrease the fatigue performance of the material. As mentioned by (2), alloys which contains Beta eutectoid elements such as Fe, Ni, Mn, Cr and Cu have depressed freezing temperatures. This situation can lead to solute segregation during ingot solidification. The segregated areas can have a length up to several millimeters. [0007] Once formel, these defects can be difficult to eliminate through all processing steps (2). The presence of This defects in their microstructure are detrimental to the mechanical behavior (3). [0008] One of the most known method used to convert the mill products in shaped components parts is forging technology. The forging technology allows to achieve the required microstructure through several thermo-mechanical processing steps. Table 1 2 highlight the processing stops in order to realize fully lamellar microstructure for the titanium Alpha - Beta alloys, such as example, titanium Ti-6A1-4A1 (grade 5), Ti6A1-2Zn-4Zr-2Mo-Si (Ti-6242) or Ti-6A1-6V-2Sn (Ti-662) (4). [0009] [Tah 'eaux 1] Steps (4) Homogenization Defomaation Recrystallizatio n Annealing lamellar mi- realized above Forging or Rcalized 30°C Realized in the Alpha crostructure the Bcta transus rolling the -50°C above + Beta phase field in Alpha-Beta during sevcral material in the Beta transus ordcr to agc alloys hours the Beta during several hardening the micro- phase field hours in order structure by the or in the to control the presence of TilAl prc- Alpha phase field Bcta grain size (----' 600 pm) (4). cipitates (4). Table 1. Processing steps for Alpha - Beta titanium alloys. [0010] To be noticed that the most important parameter in the recrystallization step is the cooling rate which will influence the grain size, Alpha lamellae, the thickness of Alpha layers at Beta grain boundaries. The Alpha lamellae and the size of Alpha colonies decrease with increasing cooling rate. The width of the Alpha lamellae decrease from 5 pm (in slowly cooled condition 1°C! min) to 0.5 pm (in fast cooling condition 100°C/min). White the Alpha colonies size decrease from 300 pm to 100 pm in the same cooling conditions. As well, very fine grains "hroken-up" structure can he ohtained in the Beta processing condition hy omitting the recrystallization steps. This is not so common commercially. 100111 As mentioned hy (4), in the final step for the annealing heat treatment, the tem- perature is more important Chan holding time hecause the temperature determines whether age hardening of the a phase hy Ti3Alparticles occurs or not. In the case of titanium alloy, Ti-6A1-4V (grade 5), aging at 500°C will precipitate the Ti3Al particles. 100121 lt is worth to mention that are critical parameters which determine the final micro- structure such as: deformation lime, deformation mode, deformation degree and the cooling rate (5). Those parameters are costly and inlluencing the shape of Beta grains, the recrystallized structure, the size of Alpha colonies and width of Alpha lamellae. 100131 Further, these shapes created hy forging technology are finished hy mechanical metal removal (machining) to the final design. From the economical point of view, the forging technology is costly in order to create a high-quality composent part. The cost is increased hy the extensively machining of the forged parts to create a complex light 3 componcnt. Thc requirement of machining is a consequence of two main rcasons. Firstly, the inahility to croate a homogenous microstructure and sccondly, the need to croate a rectilincar shapc known as "sonie shapc" for ultrasonic investigation (2). It is common to ohtain a finished part that wcight less than 10% from the starting forged block (2). [0014] Powdcr metallurgy route has bccn developcd more and more in the last &cades mainly because of thcir homogcnous chcmistry ohtaincd on powdcr particics. According to (6), powdcr metallurgical route has a major advantage in tcrrns of colt cfficicncy producing ncar net shapes with an cfficiency of 80%. This is mainly hccausc, little matcrial removal for final design is noccssary. In order to producc campiez parts, the powdcr is used hy different technologies such as additive manufacturing, mctal injection molding, press and sintcring, or hot isostatic pressing. Among thosc technologies the additive manufacturing technologies has a disadvantagc in producing industrially scalc complcx parts hccausc is limitcd hy onc hand hy the processing timc and hy othcr hand hccausc this technology requircs vcry fine sphcrical powdcr infcrior to 100 pm (7),(8),(9). [0015] Producing ncar net shapc componcnt hy pressing of the powdcr and sintcring from prc-alloycd powdcr stems a promising solution. Proccss technologies that can producc titanium powdcr such as plasma rotating cicctrodc proccss, plasma atomization and gas atomizing proccss allows to ohtain vcry cican chcmistry with very low dcfccts. Spherical powder titanium alloy grade 5 issued from the plasma rotating electrode process, gas atomizing process, or plasma atomization have a very clean chemistry with low oxygen content which can be inferior to 1500 ppm. Oxygen has a 8igniticant interstitial solubility in titanium. From one hand, the interstitial oxygen offers a strengthening effect, and by other hand it degrades the ductility. This is explained by the precipitation of Alpha from Beta leading to grain boundary alpha precipitates which are detrimental to ductility. Another reason, as mentioned by (10) is that the oxygen can induce oxygen enriched cluster or ordering and such microstructure inhomogeneities can block plastic deformation and as a consequence reduce ductility. For this reason, the oxygen content of ingot metallurgy Ti-6A1-4V is limited to 0.2% maximum (10). [0016] The spherical titanium powder with low oxygen content and their clean chemistry with low defects allow to achieve good mechanical properties if sintered density is close to the full theoretical density. Reason why, parts made from spherical powder represents a special interest for aerospace applications. Meanwhile, the spherical powder has bad behavior in teims of compaction because the resulted green body has low density and it is very difficult to reach full density after sintering. [0017] In order to be compressed, the spherical powder needs to be rnixed with a hy- drocolloid hinder hefore pressing. However, the green body has a low green strength, according to the standard ASTM B312 -14 (11) and needs carc in ordcr to be handlcd. Furthermore, in ordcr to remove the organic hinder from the green body, a dcbinding proccss is necessary to be carricd prior to the sintcring. The dcbinding proccss can be performcd during 4 to 7 hours at a range temperature from 300°C to 500°C. To be noticed that the organic hinder is not complctely evaporated in the above-mentioncd temperature range. Amines (CH-NH) or amides (CONH2) which represents 10% to 20% from the total moleculc wcight have a highcr dcbinding temperature (700°C to 900°C). Thosc molccules arc highly reactive with titanium and can lead to formation of carhides, nitrides and oxidcs in the matrix during the final densification. The presence of thosc carhides can be harmful for the mechanical bchavior and cannot match the standard requirements for acrospacc applications. [0018] The high vclocity compaction (HVC) technology is a powder compaction method which allows to ohtain high densifies of the compacted part. As mentioned hy (5), the stage of compaction is 500-1000 times faster and that the mm speed of an HVC impact machine is in the range of 2- 30 m/s. Densification in HVC is achieved hy intensive shockwaves created hy a hydraulically-operated hammer, which transfcrs the compaction energy through the compaction tool to the powdcr [1 (2). (6) has noticcd that the high velocity compaction technology is uscd to rcach high density over 99.5 % hy compaction of an agglomerated spherical powdcr with an organic hinder. Or, in the case of titanium or titanium alloy, the presence of this organic binder in his composition can be hannful for the mechanical properties due of its high reactivity with carbon, nitrogen or oxygen from their molecules. [0019] Rom the point of view of cost & performance, high velocity compaction method presents a special interest because of high densifies obtained and improved mechanical properties compared to conventional pressing and forging products. [0020] The geometry of the parts that can be produced by the high velocity compaction method is mentioned in (6). [0021] The present invention has been focused to elirninate the organic binder from the mixing and as a consequence to eliminate the debinding process from the sintering cycle in order to reduce the costs. Moreover, the present invention has been focused to improve the mechanical properties of the pressed & sintered part. The pressing has been pertormed by high velocity compaction and sintering has been realized in high vacuum. The mechanical behavior fulfills the standards requirements for aerospace applications and are very competitive compared to ingot metallurgy parts. [0022] [fig.l] PREP powder [0023] [fig.2] Amstrong powder [0024] [fig.3] Measured porosity on sample 70% PREP-30% Armstrong [0025] [fig.4] Mcasured porosity on samplc 70% PA-30% Armstrong [0026] [fig.5] Microstructure on samplc 70% PREP-30% Armstrong [0027] [fig.6] Microstructure on samplc 70% PA-30% Armstrong [0028] Sphcrical powdcr [0029] Gaz atomized proccss (GA) [0030] A gas atomization proccss for titaniutn, was dcvcloped hy Crucible Research Division of Cruciblc Materials Corporation in 1988 (13). Tn this proccss, the starting charge is induction skull tuelted undcr vacuum or an incrt gas. The molten charge is thcn hottom pourcd into an induction hcated nozzle and the rcsultant metal stream is atomized with high-prcssurc argon gas. The resulted droplets arc rapidly solidificd during cooling and allows formation of spherical powdcr particles with stnall satellites. The powdcr particles produccd hy the gas atomizing proccss lies from 10 pm till 500 pin and bas a very good flowability. The oxygcn content dépends on the size of the partici° powdcr. An average oxygcn content of 0.06 % can he ohtained on the coarser particle powdcr from 90 pm till 500 pm. While, an average oxygcn content of 0.1 % can he meet on thc smaller particic powder from 10 pm till 90 pm. The carbon, nitrogcn and hydrogcn do not &pend on the particle size. [0031] Plasma rotating électrode proccss (PREP) [0032] The plasma rotating clectrode proccss, PREP, is a centrifugal atomization proccss for making titanium pre-alloyed powdcr dcvclopcd hy Nucicar Mctals/Starmet (13). In this process, a helium plasma is used to melt the end of rapidly rotating bar. Molten droplets are spun off and solidify in flight in a helium atmosphere. The PREP powder is spherical and is presented in [fig.1]. The PREP powder has a very good flowability. The particle size is between 50 to 350 mn (10). The oxygen content on the PREP powder lies from 0.06 % till 0.15% and depends, as well, on the particle size. A higher oxygen content is meet on the smaller particle size inferior to 100 pin while a lower oxygen content is meet on the coarser powder superior to 100 pin. [0033] Plasma atomization (PA) [0034] In the plasma atomization process, a titanium wire is subrnitted to a non-transferred arc plasma torch. The high-velocity plasma melts the wire and breaks the liquid into fine droplets that solidify in flight. The powders produced by this process are spherical and has a particle size distribution from 5 pm till 250 pm. The oxygen content is inferior to 0.15% and as well depends on the particle size. [0035] Dendritic powder [0036] The Armstrong Process0 [1] is a metal halide reduction process which allows formation of a titanium powder from titanium tetrachloride gaseous stream solution introduced into reaction with a stream of Natrium liquid solution. The reaction occurs as follow: 6 [0037] TiC14(g)-F 4Na(l) -, Ti(s)-F 4NaCI(s) [0038] As well, other [notai chlorides such as aluminum trichloridc and vanadium tetra- chloride can be introduced into the rcaction stream to produce a homogencous, pre- alloyed Ti-6AI-4V. The resulted powder has a dendritic, particle morphology and is presented in [fig.2]. The powder particic size lies from few microns tilt 250 pm. The powdcr issucd from the Armstrong process have an oxygen content in the range from 0.12% till 0.2%, which matches the standard requirements for titanium grade 5 [1]. The powdcr has a high surface arca to volume ratio and as a consequence offer very gond hehavior in tenus of compressibility and green strcngth. [0039] Two spherical powdcrs issucd from the PREP process and plasma atomization, PA respectively has been tested in these experiments. [0040] The dendritic powdcr is issucd from the Armstrong process. [0041] The chemical composition and particle size for ail powdcrs arc presented in table 2. [0042] [Tablcaux2] Grade Process Ti Al V Fe C NH O Partici e size [pm] Ti-6A1- 4V PREP Rest % 6.50 4.50 0.400 0.005 0.050 0.015 0.200 88-150 Ti-6A1- 4V PA Rest % 6.29 3.94 0.148 0.009 0.016 0.012 0.074 =23 ASTM B 988-13 Min rcquircments Grade 5 828 895 10 >=25 ASTM B 348-13 Min requiremcnts Grade 5 890±30 970±30 14±2 >=25 Typical values [0071] Table 6. Mcchanical rcsults obtaincd on sintered simples PA/Armstrong and PREP/ Armstrong comparcd to grade 5 ASTM B-348 and ASTM 988-13 [0072] The mcchanical propertics as shown in table 6 shows that yicld tensile strcngth, ultimatc tensile strength and clongation obtaincd on sintered samples on both types of samplcs arc significant superior to the standard requirements ASTM B-988-14 neccssary for powder metallurgy titanium alloys parts. Morcovcr, the rcsults obtaincd in thosc tests shows that arc slightly superior to the values required by the standard ASTM B-348-13 necessary for annealed titanium parts. Thosc rcsults can be explained by a low oxygen content in sintered matcrial and homogcnous microstructure. [0073] The prcscnt invention put in evidence a vcry good cost cfficicncy. Mainly, becausc the debinding proccss is climinated from the proccss and no organic binder was uscd in the agglomeration. 11 100741 Moreover, a study accomplished by Metafensch a research institute specialized in research for metallurgy in industry for the life cycle product putted in evidence: [0075] loss of 15 % of matcrial in the atomization proccss in ordcr to producc the powder [0076] a matcrial rcmoval inferior to 3 % in ordcr to producc ncar net shapes using the MMS Scanpac® the proccss. [0077] a loss of 10 to 20 % matcrial in ordcr to producc a finishcd part hy matcrial rcmoving proccss (machining). [0078] Therefore, comparcd to forging technology which rcpresent an efficicncy of 10 % in ordcr to producc a finishcd part, the presentcd proccss, represent an efficicncy superior to 60%. References [0079] (1) K. Araci, D. Mangabhai, K. Akhtar, 9 - Production of titanium hy the Armstrong ProcessO, Editor(s): Ma Qian, Francis H. (Sam) Frocs, Titanium Powdcr Mctallurgy, Butterworth-Heinemann, 2015, Pages 149-162, ISBN 9780128000540 [0080] (2) G. Liitjering, J.C. Williams "Titanium" second cdition, 3 - tcchnological aspects Springcr, 2007, pagcs 53-173, ISBN 978-3-540-71397-5 [0081] R. Boycr, E.W. Collings, and G. Wclsch: "Materials Properties Handbook: Titanium Alloys", 1994, ISBN 978-0-87170-481-8 [0082] (4) G. Liitjering, J.C. Williams "Titanium" second cdition, 5 - Alpha + Bcta alloys Springcr, 2007, pages 203-258, ISBN 978-3-540-71397-5 [0083] (5) N. Gcy, M. Humbert, M.J. Philippe, Y. Cornbres, Investigation of the a- and (3- texture cvolution of hot rolled Ti-64 products, Matcrials Science and Engineering: A, Volume 219, Issues 1-2,1996, Pages 80-88, ISSN 0921-5093 [0084] (6) Chrier Aslund, "Multilevcl parts from agglotncratcd sphcrical powder", patent 1352015239045 [0085] (7) F. Nobuo: "Titanium- Based Powdcr, Titanium bascd ingot obtaincd by fusing titanium- bascd powder, and titanium bascd sintered article ohtained hy sintcring titanium-bascd powder" patent JP2018145467. [0086] (8) F. Nobuo: "Titanium bascd powder and ingot and sintcred ingot thcreor, patent U52018021854 [0087] (9) S. Knittek, G. Fribourg. "Composition for manufacturing parts from titanium aluminide by powder sintering, and manufacturing method using such a composition" patent US2018112293 [0088] (10) M. Yan, H.P. Tang, M. Qian, 15 - Scavenging of oxygen and chlorine from powder metallurgy (PM) titanium and titanium alloys, Editor(s): Ma Qian, Francis H. (Sam) Froes, Titanium Powder Metallurgy, Butterworth-Heinemann, 2015, Pages 253-276, ISBN 9780128000540 12 [0089] (11) ASTM B312 -14 Standard Test Method for Green Strength of Specimens Compacted from Metal Powders, ASTM International, West Conshohockcn, PA, 2014 [0090] (12) P. Skoglund, M. Kcjzchnan, 1. Haucr "High density components PM hy high vclocity compaction" PM2 TEC, Orlando, USA, 2002 [0091] (13) C.F. Yolton, Francis H.Froes, 2 - Conventional titanium powdcr production, Editor(s): Ma Qian, Francis H. (Sam) Frocs, Titanium Powdcr Mctallurgy, Butterworth-Heinemann, 2015, Pages 21-32, ISBN 9780128000540. [0092] (14) ASTM B311-17, Standard Test Method for Dcnsity of Powdcr Metallurgy (PM) Materials Containing Less Than Two Percent Porosity, ASTM International, West Conshohockcn, PA, 2017 [0093] (15) ASTM El 409-13, Standard Test Mcthod for Determination of Oxygen and Nitrogen in Titanium and Titanium Alloys hy Inert Gas Fusion, ASTM International, West Conshohocken, PA, 2013 [0094] (16) ASTM El 447-09(2016), Standard Test Mcthod for Deterrnination of Hydrogen in Titanium and Titanium Alloys hy Inert Gas Fusion Thermal Conductivity/Infrared Detection Mcthod, ASTM International, West Conshohocken, PA, 2016 [0095] (17) ASTM El 941-10(2016), Standard Test Mcthod for Deterrnination of Carbon in Rcfractory and Rcactivc Metals and Thcir Alloys hy Combustion Analysis, ASTM International, West Conshohocken, PA, 2016, [0096] (18) ASTM B988-13 Standard spécification for powder mctallurgy titanium and titanium alloy structural component, ASTM International, West Conshohocken, PA, 2013. [0097] (19) ASTM B-348-13 Standard specification for titanium and titanium alloys bar and billets, ASTM International, West Conshohocken, PA, 2013. 13 REVENDICATIONS[Revendication 1] A process for compressing an agglomerated spherical titanium alloy powder with dendritically titanium alloy powder, characterized in that the agglomcratcd powder is pressed by high velocity compaction with a ram spccd superior to 2 m/s to a green body having high green density superior to 78%. [Revendication 2] A process according to daim 1, wherc the spherical powder is in amount of 60% to 90% in weight and the dendritically powder is in amount 10% to 40%. [Revendication 3] A process according to daim 1 and 2, where there is 110 used internai binder. [Revendication 4] A process according to the daim 1 to 3, wherein the ram speed is superior to 4 m/s and a pressure of 600-1500 MPa. [Revendication 5] A process according to the daim 1 to 4, wherein the spherical titanium alloy powder is obtained from the PREP process, the PA process or the GA process. [Revendication 6] A process according to the claim 1 to 5, wherein the dendritically titanium alloy powder is obtained from the Armstrong process. [Revendication 7] A process for the preparation of the sintered product from the ag- glomerated spherical powder and dendritically powder with no organic binder pressed by high velocity compaction with a ram speed superior to 2 mis and a pressure of 600 - 1500 MPa and the sintering is realized in a reducing atmosphere with a vacuum pressure in the range 104Torr to 10 - Ton and the sintering temperature is preformed in the range 1200°C 1350°C in accordance with any daims 1 to 6 and said green body is sintered to full or near full theoretical density, ie at least 99% of the full theoretical density, preferably at least 99.9%.