60NiTi合金的热压缩变形与显微组织演变

采用Gleeble-3500热模拟试验机对在变形温度500~650℃和应变速率0.001~1 s^(-1)条件下的60NiTi合金进行热压缩变形,分析其热变形行为和显微组织,建立变形本构模型,绘制热加工图。结果表明,当压缩温度升高或应变速率降低时,峰值应力减小。合金的热变形激活能为327.89 k J/mol,热加工工艺参数为变形温度600~650℃和应变速率0.005~0.05 s^(-1)。当变形温度升高时,合金的再结晶程度增大;当应变速率增大时,位错密度和孪晶数量增大,Ni3Ti相易于聚集;Ni3Ti析出相有利于诱发合金基体的动态再结晶。动态回复、动态再结晶和孪生是60NiTi合金热变形的主要机制。

渗硼对60NiTi合金表面组织与性能的影响

60NiTi合金具有高硬度、低弹性模量、耐腐蚀等优点,被认为是极具应用潜力的新型航空航天轴承材料。为了进一步提升60NiTi合金的耐磨特性,本文利用固相渗硼技术对其进行了表面改性处理,研究了改性层的显微结构特征及其相结构的热力学形成机理,分析了表面改性对合金力学与摩擦学性能的影响规律。结果表明,60NiTi经1000℃-5 h渗硼处理后形成了TiB_(2)/NiTi_(2)+TiB_(2)/Ni_(3)Ti的梯度涂层结构,整体厚度约20μm。渗硼后样品的表面硬度从420 HV_(0.2)提升至2600 HV_(0.2),20 N外加载荷作用下的平均摩擦系数和磨损率分别降低了约39%和92%。由于摩擦热的作用,渗硼样品表面会生成具有润滑作用的氧化硼相,因此呈现出良好的减摩耐磨特性。

冷却方式与时效温度对60NiTi合金硬度和组织的影响

系统研究了冷却方式、时效温度对60NiTi合金硬度和组织的影响,结果表明:相比于退火处理试样,正火或淬火处理能显著提高合金的硬度;正火试样300℃时效处理能进一步提高合金硬度,而400,500,600℃时效处理使合金硬度降低,其中600℃时效处理合金硬度下降最显著;通过正火+300℃时效处理后合金的硬度由铸态试样的31 HRC提高到60 HRC。金相与X射线衍射(XRD)结果表明,正火和淬火处理后的60NiTi合金晶粒中没有粗大针状析出相形成。获得均匀细小的组织并避免Ni_(4)Ti_(3)相在冷却及时效过程中粗化并转变成Ni_(3)Ti相是得到高硬度60NiTi合金的关键。

Wear Resistance and Indentation Behavior of Equiatomic Superelastic TiNi and 60NiTi

Indentation and reciprocating wear tests are carried out to study dent and wear resistance of superelastic Ti-Ni alloys. The effect of loading rate on the superelastic behavior of TiNi under indentation loading is investigated and compared to a new generation of shape memory alloys, i.e., 60NiTi. Only limited amount of work has been done to investigate the dependency of superelasticity on loading rate of TiNi under localized compressive loads, but much work is directed towards understanding the effect of strain rate on tensile properties. Understanding the superelastic behavior helps to employ superelastic alloys in applications where high impact loading is expected as in bearings and gears. In the present study, it is found that dent resistance of Ti-Ni alloy is not significantly affected by loading rate (within the employed loading conditions). It has also been found that new-generation 60NiTi alloy exhibits superior wear and dent resistance, as well as higher hardness compared to equiatomic TiNi.

添加Zr的60NiTi合金的热处理工艺优化

60NiTi合金具有高硬度、低密度和耐磨等优异的性能,在航空航天领域有广泛的应用前景。为了进一步提高60NiTi合金的力学性能,研究了Zr的添加及热处理工艺对60NiTi合金组织与硬度的影响。结果表明:Zr的添加提高了60NiTi合金的硬度并使其组织更加均匀。此外,在炉冷、空冷、油冷和水冷4种不同的冷却方式中,炉冷60NiTiZr合金中存在大量粗大的析出相,硬度也最低。冷却速度最快的水冷处理的60NiTiZr合金的硬度最高,且能够避免粗大析出相形成,但存在残余应力较大的问题。对水冷60NiTiZr合金在300~600℃温度范围进行时效处理,发现随时效温度的升高,合金的硬度先升高后降低,且在500℃时效时硬度达到最高。进一步对水冷60NiTiZr合金在500℃进行不同时间的时效处理,发现时效2 h后合金硬度达到峰值(61.7 HRC),时效后期还出现缓慢的二次硬化现象。

热处理对铸态60NiTi合金第二相析出与硬度的影响

利用OM、XRD、SEM、EDS和DSC等分析测试手段研究了不同热处理方式对60NiTi合金中第二相析出,及其对马氏体转变和硬度的影响。结果表明:固溶后水淬处理能显著提高铸态60NiTi合金的硬度,但炉冷处理却显著降低合金的硬度。400℃时效略微降低固溶后水冷合金的硬度,但长时间时效对硬度的影响不大。Ni_3Ti相的大量固溶是固溶水冷处理显著提高铸态合金硬度的原因,而固溶后炉冷合金硬度下降则来源于更多Ni_3Ti相的析出。60NiTi合金的硬度取决于马氏体转变发生的难易程度。

SPS烧结压力对60NiTi合金显微组织及摩擦学性能的影响

采用放电等离子烧结(SPS)法在1000℃制备60NiTi合金,研究烧结压力对60NiTi合金的显微组织、显微硬度和摩擦学性能的影响规律;采用X射线衍射仪、扫描电镜分析60NiTi合金的显微组织,采用显微硬度仪评价60NiTi合金的显微硬度,通过摩擦磨损试验机研究60NiTi合金摩擦学性能,利用三维白光轮廓仪分析磨痕形貌并计算60NiTi合金的磨损体积,采用扫描电子显微镜分析磨痕表面形貌。实验结果表明:在25 MPa烧结压力下,通过放电等离子烧结法制备的60NiTi合金显微组织均匀,主要为Ni_(3)Ti相和Ni3Ti相。随着烧结压力增加,60NiTi合金的显微硬度随之增加,且在50 MPa烧结压力时合金的显微硬度HV_(0.2kg)达到最大值5233.2 MPa。60NiTi合金的磨损率和磨痕深度随着烧结压力的增加而减小,在50 MPa烧结压力时,60NiTi合金的磨损率和磨痕深度最小,分别为0.76×10^(-5)mm^(3)/(N·m)、15μm,其磨损机制为磨粒磨损与黏着磨损共同作用机制。

航天轴承新贵:60NiTi合金

在NiTi系合金大家族中,等原子比的NiTi合金具有形状记忆效应和超弹性。相比于等原子比NiTi合金,60NiTi合金不会发生热弹性马氏体相变,不具有形状记忆效应和超弹性,但是它在硬度、耐腐蚀性和弹性性能等方面具有出众的潜能,在航天领域上展现了良好的应用前景。固溶态60NiTi合金同时具备结构稳定性、超强的耐腐蚀性、出色的耐磨性,已成为航天轴承候选新材料。

Tribological performance of hydrogenated diamond-like carbon coating deposited on superelastic 60NiTi alloy for aviation selflubricating spherical plain bearings

It is imperative to develop a novel matching of metallic substrate and self-lubricating coating for aircraft spherical plain bearing in a wide range of service conditions.As a new type of superelastic material,60NiTi alloy meets the performance requirements of aerospace bearing materials,but exhibits poor tribological performance,especially under the conditions of dry sliding friction.A Hydrogenated Diamond-Like Carbon(H-DLC)coating was deposited on the 60NiTi alloy to improve its tribological performance.The microstructure and mechanical behavior of the 60NiTi alloy and its H-DLC coating were explored.Results show that improvement of friction and wear performance of the H-DLC coating deposited on the 60NiTi substrate is mainly achieved by graphitization at the friction interface and the transfer film produced on the counterpart ball.The increased friction load leads to intensification of graphitization at the friction interface and formation of continuous and compact transfer film on the surface of the counterpart ball.

Heat treatment of hot-isostatic-pressed 60NiTi shape memory alloy:Microstructure,phase transformation and mechanical properties

60NiTi alloy is considered to be a promising material for specialized bearing and gear applications due to its high hardness,strength,and low modulus.However,fabricating 60NiTi through conventional processing methods is challenging due to the brittleness and poor workability.In this study,60NiTi with high relative density was successfully fabricated directly from pre-alloyed powder through hot isostatic pressing.The effects of solution and aging treatments on microstructure and mechanical properties were systematically studied by advanced characterization techniques.The hot-isostatic-pressed 60NiTi showed low average hardness and elastic strain due to the formation of a soft Ni_(3)Ti phase and B2 NiTi matrix.Solution treatment above 1000℃dissolved the Ni_(3)Ti phase and promoted the formation of nanoscale Ni_(4)Ti_(3)precipitates,which significantly improved the hardness,strength,and elastic strain of 60NiTi.The formation of the Ni_(4)Ti_(3) phase can be mainly attributed to the driving forces induced by the chemical supersaturation and mechanical stress concentration.Finally,the phase transformation mechanisms during heat treatment and compression test were discussed.

Loading rate and holding load dependent room temperature nanoindentation creep behavior of 60NiTi alloy:Individual and coupling effects

60NiTi alloy is highly promising for aerospace bearings and mechanisms.Shock load that is inevitably generated during launching process brings about an quick loading process and transient load duration,and may further results in an unnoticed but detrimental creep deformation.On this account,the nanoindentation creep behavior of solution-treated 60NiTi alloy at room temperature and the corresponding influencing mechanism were studied.The results show that creep displacement was dominated by strain rate at the very beginning of holding stage.Strain rate and flow stress at the very beginning of holding stage were increased with an increased loading rate but declined with increasing holding load or with simultaneously increasing loading rate and holding load.The underlying mechanisms were provided as nucleation and absorption of geometrically necessary dislocations(GNDs)associated with strain gradient plasticity theory rather than the model based on the consumption of creep deformation at loading stage.

Enhanced micro/nano-tribological performance in partially crystallized 60NiTi film

The microstructure,mechanical and micro/nano-tribological properties of the 60NiTi film annealed at different temperature were investigated.The results reveal that annealing as-deposited 60NiTi film at 300,375,and 600℃ for 1 h leads to structural relaxation,partial crystallization and full crystallization,respectively.Compared with the structurally relaxed structure,the partially crystallized structure exhibits increased hardness but decreased elastic modulus.This is because that the elastic modulus is reduced by Voigt model while the hardness is improved by composite effect.Due to the highest hardness and ratio of hardness to elastic modulus(H/E),the partially crystallized 60NiTi film has the lowest penetration depth and residual depth(i.e.,groove depth).Besides,the results also reveal that ductile plowing is the dominant wear mechanism for all the annealed 60NiTi films.Under the condition of the ductile plowing,coefficient of friction and wear resistance are related to penetration depth and residual depth,respectively.Therefore,the partially crystallized 60NiTi film shows the best tribological performance at the micro/nano-scale.The current work not only highlights the important roles of hardness and H/E in improving the micro/nano-tribological properties but also concludes an efficient and simple method for simultaneously increasing hardness and H/E.

NiTi合金与增材制造——下一代航空航天轴承用材料

近年来,NiTi合金材料因具有优异的形状记忆效应、超弹性及良好的耐热、耐磨、耐蚀等性能,被广泛应用于航空航天等领域.综述了对航空航天轴承用材料的性能要求.分析了目前国内外常用的轴承材料的性能.介绍了60NiTi合金的超弹性和摩擦磨损特性.详细论述了NiTi合金常用的制造工艺及其优缺点.阐述了60NiTi合金的研方向和应用前景。

NiTi60合金耐磨材料显微组织及硬度的研究

通过光学金相和显微硬度试验的分析方法,研究了热处理对NiTi60耐磨材料性能的影响。实验表明,NiTi60耐磨材料经过不同的热处理工艺后材料的硬度变化明显,在800℃×30min/WQ+300℃×15min/WQ热处理工艺制度下其硬度值最高;800℃固溶处理后,随着时效温度的升高,鱼骨状晶逐渐消失,线状晶逐渐增多,但黑色颗粒状晶逐渐减少,基体不再得到强化,材料显微硬度明显降低。