TiNbZrTa β titanium alloys and super-elastic characteristics of cold-deformation mechanism

Title: TiNbZrTa β titanium alloys and super-elastic characteristics of cold-deformation mechanism ofAuthor: Li-Qiang WangDegree-granting units: Shanghai Jiaotong UniversityKeywords: β titanium alloy;; cold deformation;; texture;; precipitates;; grain refinement;; super-elasticSummary:

Since titanium has a high biocompatibility, low density, high strength, corrosion-resistant fluids, etc., are widely used in medical fields. The low modulus of elasticity and non-toxicity in the body element of β titanium implants and other medical materials has broad application prospects. Starting from the 1990s, research and development of new β titanium materials on the Neodymium Magnets development of a medical focus. For now, Nb, Ta, Zr and Sn and other elements have good biocompatibility, the body has less toxicity. Shape memory and super-elastic properties of the optimization for the application of such alloys is of great significance. In general, the martensite twins, grain orientation and texture, grain size of the precipitates and super-elasticity has important implications. For such alloys in terms of cold deformation and not super-elastic mechanism of the system, in-depth. Research in the cold deformation process of martensite transformation and deformation characteristics of sub-structure, for further discussion of these super-elastic alloy, shape memory effect has an important role. Studied in this paper is TiNbZrTaβ titanium alloy. Select a different cold deformation after deformation, cold deformation mechanism of alloy, and the amount of martensite transformation characteristics and mechanical properties were studied. By cold deformation and heat treatment on texture analysis and discussion of the formation of texture features. Analysis of texture anisotropy on the impact of super-elastic alloy law. In addition, samples of cold deformation heat treatment at different temperatures to study the aging process of precipitation relative to the shape memory effect and mechanical properties and impact.

In the cold deformation titanium TiNbZrTaβ depth and systematic study of the characteristics on the basis of adding rare earth elements in the alloy, in the purification of rare earth added to the matrix alloy, grain refinement to improve the alloy's shape memory http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets effect, while reducing titanium matrix oxygen content in the alloy of rare earth oxides to generate hard phase (RE2O3). Studies have shown that, TiB titanium matrix composite reinforcements in one of the best, can effectively improve the strength of titanium matrix composites. The reinforcement of β titanium shape memory effect is rarely reported on. The use of vacuum arc melting technique, the distribution of a small amount of synthetic TiB, La2O3 particles of β-titanium alloy, the alloy can get a good strength and shape memory effect. Adding different amounts of LaB6 on TiNbZrTaβ titanium super-elastic and mechanical properties will also serve as the focus of this paper. The use of Ti and LaB6 reaction by vacuum arc melting, in situ synthesized TiB and rare earth oxides La2O3 enhanced titanium matrix composites, studied the reinforcement particles in the alloy refinement of the role of adding different amounts of LaB6 on the alloy mechanical properties and shape memory effect in improving the role.

The major findings are as follows:

One-way cross-rolling and rolling two different deformation studies under different deformation characteristics of the material microstructure, after analysis of the different deformation characteristics of martensitic variants. The study found that in the one-way rolling process, the martensite boundary by a straight needle with a small lamellar structure gradually changes as the "butterfly-like" martensite morphology for the appearance of thick parallel to the rolling direction of film body, and with the cold deformation rates continue to increase, this thick slice along the rolling direction of the body was interwoven like expansion. Martensite in the process of cross-rolling and unidirectional rolling the changes of a similar law, but because of the role of cross-rolling shear stress, so there is no obvious directional growth of martensite. In the one-way rolling process, when the rate of 99% cold deformation, the martensite transformation of the maximum amount of 78.93% or so. The cross-rolling process, when the rate of 40% cold deformation, martensite transformation reached 79.63%, and with the cold deformation increases, the relative content of martensite remained constant, cross-rolling process features more conducive to stress in the martensitic transformation. Making the organization more in all directions evenly. In the cold rolling process, with the cold deformation rate increases, the strain-induced martensite has undergone nucleation, growth, and stability of the process. Martensite deformation mechanism involved in martensitic variants occur within the micro-twins and micro-twins grew up → merged and re-orientation → twinned martensite variants within the new introduction.

Generated in the process of cold deformation texture of β phase and the strain-induced martensite α "phase texture of the material modulus of elasticity and super-elastic characteristics have an important impact on the elastic modulus and super-elastic anisotropy is due to texture due to anisotropy in the rolling one-way process, with the cold deformation rate increases, the emergence of a strong {100} β <011> β texture in 90% cold deformation of the specimen in apparent strain induced (200) α "<010> α" martensite texture. makes the emergence of different texture in all directions along the specimen strain showed significant changes in anisotropy.

In the cold deformation heat treatment process, the metastable phase at 573K appeared ω, heat treatment at 673K ​​to 873K when α phase. After the 573K effect, ω small dispersed phase alloy increases the critical slip stress can significantly increase the super elastic alloy. 99% of the sample at 873K cold deformation after heat treatment 1.2ks along the rolling direction, and was 45 ° to the rolling direction and perpendicular to the rolling direction of the cold rolling texture of 99% compared to little change. Appear strong {100} <011> texture. Cold deformation of the sample heat-treated at 1223K 1.2 ks after cold deformation texture into {112} <011> recrystallization texture. Cold deformation of {100} <011> texture in the heat treatment process gradually transformed into {112} <011> recrystallization texture. Recrystallization and cold when the change form the core samples have basically the same position is due to the nucleation of recrystallization by grain boundary bows out, grew up in sub-grain boundary migration mechanisms in the formation of the core deformation of the matrix with the same bit to. To 1223K 5.5% tensile deformation heat treatment specimen strip arise from the collaborative deformation twins and stress-induced martensite needle. This stress-induced martensite produced by heating into the parent phase, the alloy apparent shape memory effect.

Using in-situ technology, synthesized TiB and β titanium Re2O3, to improve the alloy's shape memory effect and superelasticity. Base material used in this paper does Ti-35Nb-3Zr-2Ta alloy. Adding mass fraction in the test were 0.1%, 0.2%, 0.3%, 0.4% and 0.5% of the LaB6 powder, generated through the in situ reaction and La2O3 TiB whisker reinforcement particles. Add in the 0.1% LaB6 samples, in situ reaction of TiB whiskers mainly on the grain boundaries, making the strength of the specimen significantly increased. With the increase in the amount of added LaB6 can be observed more TiB whiskers and La2O3 spherical particles. Gradually increasing the grain refinement of La2O3 particles, making the 0.5% LaB6 sample grain size refinement added to 12um. 0.1% and 0.2% LaB6 add samples, the material exhibits good elastic strain and ultra-pure elastic strain. Add in the 0.5% LaB6 sample, due to grain refinement, making the sample value of the largest super-elastic strain. Reaction process in situ TiB whiskers produced an increase of the critical slip stress. Thus, in the drawing process, the lower the applied stress can make the sample occurred opposite martensitic transformation β, this rising super-elastic properties of the alloy makes the application of gradually extended to the super-elastic fastener applications .

Observed in situ tensile test in (TiB + La2O3) / (Ti-35Nb-3Zr-2Ta) sample the major micro-deformation mechanism. At low strain, the tensile force along the direction of linear dislocation nucleation. As the strain increases, the nucleation of dislocation experienced, starting and interact together in several stages. With the slip of dislocations, dislocation around the self-inducing type of collaboration like twin martensite. Observed throughout the drawing process to {111} twins and (001) compound twin chip. This (001) compound twin-chip with the strain rate increases gradually to the adjacent {111} twinned lath matrix expansion and growing up to the original {111} twinned lath organization the same size.Degree Year: 2009