【作者】 王启；

【导师】 贺志荣；

【作者基本信息】 陕西理工学院 ， 材料加工工程， 2011， 硕士

【摘要】 本文以Ti-50.8Ni-0.3Cr（原子%）形状记忆合金（SMAs）为研究对象,用X射线衍射仪、示差扫描量热仪、拉伸实验、光学显微镜和电子显微术研究了退火和时效工艺对该合金相变、形变行为和显微组织的影响。结果表明:退火温度T_an对Ti-50.8Ni-0.3Cr合金的相变行为有着显著影响。T_an=350～450℃时,合金发生A→R/R→A型可逆相变;T_an=500℃时,合金发生A→R→M/M→R→A型相变;T_an=550～600℃时,合金发生A→R→M/M→A型相变;T_an=650～800℃时,合金不发生相变。随时效时间t_ag延长,300℃时效态合金的相变类型为A→R/R→A,400℃时效态合金发生由A→R/R→A向A→R→M/M→R→A转变,500℃时效态合金发生由A→R→M/M→R→A向A→R→M/M→A转变。随T_an升高,合金的R相变温度T_R先升高后降低,M相变温度T_M升高,M相变热滞ΔT_M降低。合金经300～500℃时效后,T_R⁴⁰⁰>T_R³⁰⁰>T_R⁵⁰⁰。随t_ag延长,T_R、T_M先快速升高后趋于稳定,ΔT_M先快速降低后趋于稳定。另外,退火和时效态合金的R相变热滞ΔT_R均在4℃左右。在退火处理过程中,由于Ti-50.8Ni-0.3Cr合金的供货态为冷加工态,退火时将发生回复与再结晶。T_an=350～500℃时,合金为回复阶段,显微组织仍呈纤维状;T_an=550～580℃时,合金发生再结晶,纤维组织逐渐变成无畸变等轴晶粒;T_an=590～800℃时,为晶粒长大阶段,显微组织为粗大且大小不均匀的晶粒;随T_an升高,合金的应力诱发马氏体临界应力σ_M先降低后升高,随后趋于稳定;残余应变εR在T_an=350～590℃时变化不大,始终保持在较低的水平,当T_an>590℃时,则急剧升高。另外还可以得出,合金的开始再结晶温度在570℃左右,要使该合金获得良好的超弹性,退火温度应低于再结晶温度。在固溶时效处理过程中,800℃固溶淬火态合金塑性良好,适合于冷成形加工。随时效时间t_ag延长,300℃和400℃时效态合金的抗拉强度σ_b³⁰⁰和σ_b⁴⁰⁰先急剧增大后趋于稳定,且σ_b³⁰⁰ <σ_b⁴⁰⁰,延伸率δ_k³⁰⁰和δ_k⁴⁰⁰先急剧减小后趋于稳定;500℃时效后,σ_b⁵⁰⁰先急剧减小后趋于稳定,δ_k⁵⁰⁰先急剧增大后趋于稳定。随t_ag延长,300℃和400℃时效态合金的应力诱发马氏体临界应力σ_M300和σ_M400均逐渐减小,而σ_M500则先减小后增加再减小,极大值在t_ag=10h时取得。此外,随t_ag延长,300℃时效态合金的Ti3Ni4析出相呈细小颗粒状弥散分布;400℃时效态合金的Ti3Ni4析出相由颗粒状演变成透镜状;500℃时效态合金的Ti3Ni4析出相发生由透镜状向针状再向粗片状演变。时效温度对Ti3Ni4析出相形态的影响效果比时效时间显著。随试验温度Td的升高,退火和时效态Ti-50.8Ni-0.3Cr合金弹簧的应力诱发马氏体相变临界切应力τ_M均逐渐升高;其中,随T_an的升高,τ_M先降低后升高;随t_ag延长,300℃时效态合金弹簧的τ_M逐渐降低。随循环次数N增加,合金弹簧应变恢复率先快速衰减,后趋于稳定;预循环可增强弹簧元件SE的稳定性。更多还原

【Abstract】 Effects of annealing and aging treatment on transformation, deformation and microstructure of Ti-50.8Ni-0.3Cr（% atomic fraction）Shape Memory Alloys （SMAs） were investigated by X-ray diffraction, differential scanning clorimetry, tensile test, optical microscopy and electonic microscopy in this paper. The results are as follows.A→R/R→A type reversible transformation occurred in 350～450℃annealed alloy upon cooling/heating, A→R→M/M→R→A occurred in 500℃annealed alloy, A→R→M/M→A occurred in 550～600℃annealed alloy, and no transformation occurred in the above 650℃annealed alloys. With increasing aging time, the transformation type of 300℃aged alloy is A→R/R→A, the one of 400℃aged alloy is from A→R/R→A to A→R→M/M→R→A, and the one of 500℃aged alloy is from A→R→M/M→R→A to A→R→M/M→A. With increasing T_an, the R transformation temperature T_R increases first and then decreases, the M transformation temperature T_M increases, and the M temperature hysteresiseΔT_M decreases. After aging at 300～500℃, the T_R⁴⁰⁰>T_R³⁰⁰>T_R⁵⁰⁰. With increasing t_ag, the T_R and T_M increases first and then tend to stable, and theΔT_M decreases first and then tend to stable. Futhermore, the R temperature hysteresis in the annealed and aged alloys is all about 4℃.The Ti-50.8Ni-0.3Cr alloys took place the recovery and the recrystallisation procedure during annealing treatment due to the cold working as recived. When T_an =350～500℃, the alloy is at the recovery procedure, the microstructure is fibriform; when T_an =550～590℃, the alloy is at the recrystallisation procedure, the microstructure turns to the unstrained equi-axed grains; When T_an =600～800℃, the alloy is at grain growth procedure, the microstructure became larger and asymmetrical grain. With increasing T_an, the critical stress for inducing martensiteσ_M descends firstly and then rises; when T_an =350～590℃, the residual strainεR has no obvious change and keeps at a low value all the time. When T_an >590℃, theεR rises rapidly. Furthermore, the recrystallisation temperature of the alloy is about 570℃. In order to getting excellent SE, the annealing temperature of the alloy should be below recrystallization temperature. After solution and aging treatment, the 800℃solution annealed Ti-50.8Ni-0.3Cr alloy exhibits well plasticity and is advant_aged to cold deformation. With increasing t_ag, the tensile strengths (σ_b³⁰⁰ andσ_b⁴⁰⁰) of 300℃and 400℃aged alloys increase sharply firstly and then tend to a stable value, here,σ_b³⁰⁰ <σ_b⁴⁰⁰; the % elongationδ_k³⁰⁰ andδ_k⁴⁰⁰ decrease sharply firstly and then tend to stable. After aging at 500℃, theσ_b⁵⁰⁰ decreases sharply firstly and then tends to stable, theδ_k⁵⁰⁰ increases sharply firstly and then tends to stable. With increasing t_ag, the critical stress for inducing martensitic transformationσ_M300 andσ_M400 of 300℃and 400℃aged alloys decrease gradually, whileσ_M500 decreases firstly and then increases sharply, finally decreases gradually again and the maximum is reached at t_ag=10h. Furthermore, with increasing t_ag, the morphology of Ti3Ni4 precipitates of 300℃aged alloy is fine particle shape; the one of 400℃aged alloy evolves from particle to lenticular shape; the one of 500℃aged alloy evolves from lenticular to needle to plate shape. The influencing of the aging temperature on the morphology of Ti3Ni4 precipitates is more significant than that of the aging time.With increasing the test temperature Td, the critical shear stress for inducing martensitic transformationτ_M of both the annealed and aged Ti-50.8Ni-0.3Cr alloy spring increase gradually; with increasing T_an, theτ_M decreases firstly and then increases; with increasing t_ag, theτ_M of 300℃aged alloy spring decreases gradually; with increasing the stress-strain cycles numbers N, the strain recovery ratio declines quickly at the beginning and then slowly.更多还原