超高压时效对TiNi形状记忆合金显微组织及马氏体相变的影响
发布时间：2018-12-14 21:30
【摘要】：TiNi合金因具有形状记忆效应及良好的力学性能而广泛应用于航空航天、民用工业领域;超高压影响材料新相的形成,超高压不同时效工艺对TiNi合金组织性能有着重要影响,采用X射线衍射技术、透射电子显微镜、差示扫描量热、拉伸试验、硬度测试系统研究超高压不同时效工艺对Ti-51(at%)Ni合金显微组织形貌、马氏体相变及力学性能的影响。试验结果表明,超高压时效,随着温度的升高或时间的增长,尺寸逐渐增大,Ti3Ni4析出相逐渐由颗粒状长大为椭圆透镜状、椭圆薄片状,最终长大为粗片状,随着压力增大,析出相尺寸减小;超高压导致晶粒内部形成高密度位错,高压时效晶界处与晶粒内部析出相分布并无明显差异;随着时效温度的升高,合金由两步相变转变为一步相变,随着时效时间的增长,合金由两步相变逐渐转变为三步相变,随着压力的增大,合金由一步相变转变为两步相变,进一步转变为三步相变;室温下拉伸,高压不同温度时效抗拉强度在600℃达到最大为960MPa,延伸率最大为19.2%,硬度在500℃达到最大为382.4HV;高压不同时间时效,抗拉强度在2h达到最大为1150MPa,延伸率最大为18%,硬度在5h达到最大为433.9HV;不同压力时效,抗拉强度在5.5GPa达到最大为960MPa,延伸率在1GPa达到最大为22%,硬度在3GPa达到最大为404.7HV。试验分析表明,高压使扩散系数减小,高压时效下Ti3Ni4析出相的尺寸小于常压时效析出相的尺寸,随着压力的增大,Ti3Ni4析出相显著细化;超高压导致高密度位错,为析出相形核提供动力,使得析出相晶内与晶界分布没有明显差别;Ti3Ni4析出相与基体呈共格或半共格关系,使局部应力不均,导致R相变产生;Ti3Ni4析出相导致内部成分不均匀分布,使得马氏体相变温度发生变化,导致三步相变产生;超高压不同工艺时效TiNi合金,析出相细化及高密度位错的形成改善了力学性能。在综合分析超高压不同时效工艺对TiNi合金显微组织结构及马氏体相变、力学性能的影响规律和机制的基础上,确定了高压时效与常压时效不同的根本原因在于高压使扩散系数减小以及产生高密度位错,导致Ti3Ni4析出相分布及大小不同,进一步影响马氏体相变及力学性能。
[Abstract]:TiNi alloy is widely used in aerospace and civil industry because of its shape memory effect and good mechanical properties. Ultra-high pressure affects the formation of new phase of TiNi alloy, and different aging processes have an important effect on microstructure and properties of TiNi alloy. X-ray diffraction technique, transmission electron microscope, differential scanning calorimetry, tensile test are used. The effects of different aging processes on the microstructure, martensite transformation and mechanical properties of Ti-51 (at%) Ni alloy were investigated by hardness measurement system. The experimental results show that with the increase of temperature or time, the size of Ti3Ni4 precipitates gradually increases, and the precipitates of Ti3Ni4 gradually grow from granular to elliptical lens, elliptical thin slice, and finally grow to coarse flake, and increase with the increase of pressure. The size of precipitated phase decreases; High density dislocation is formed in the grain due to ultra-high pressure, and there is no obvious difference between the precipitation phase distribution at the high pressure aging grain boundary and that in the grain. With the increase of aging temperature, the alloy changes from two-step transformation to one-step phase transformation, with aging time increasing, the alloy gradually changes from two-step phase to three-step phase transition, and with the increase of pressure, the alloy changes from one-step phase to two-step phase transition. Further transformation into three-step phase transition; At room temperature, the maximum aging tensile strength at 600 鈩，
本文编号：2379355
[Abstract]:TiNi alloy is widely used in aerospace and civil industry because of its shape memory effect and good mechanical properties. Ultra-high pressure affects the formation of new phase of TiNi alloy, and different aging processes have an important effect on microstructure and properties of TiNi alloy. X-ray diffraction technique, transmission electron microscope, differential scanning calorimetry, tensile test are used. The effects of different aging processes on the microstructure, martensite transformation and mechanical properties of Ti-51 (at%) Ni alloy were investigated by hardness measurement system. The experimental results show that with the increase of temperature or time, the size of Ti3Ni4 precipitates gradually increases, and the precipitates of Ti3Ni4 gradually grow from granular to elliptical lens, elliptical thin slice, and finally grow to coarse flake, and increase with the increase of pressure. The size of precipitated phase decreases; High density dislocation is formed in the grain due to ultra-high pressure, and there is no obvious difference between the precipitation phase distribution at the high pressure aging grain boundary and that in the grain. With the increase of aging temperature, the alloy changes from two-step transformation to one-step phase transformation, with aging time increasing, the alloy gradually changes from two-step phase to three-step phase transition, and with the increase of pressure, the alloy changes from one-step phase to two-step phase transition. Further transformation into three-step phase transition; At room temperature, the maximum aging tensile strength at 600 鈩，
本文编号：2379355
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