高强、导电Cu-Ti系合金中的相变规律及其对性能的影响

Among the substitute materials for Cu-Be alloy, Cu-Ti system alloys are specially attractive because their mechanical and physical properties were found to be comparable to those of the Cu–Be alloys with combination of higher elevated temperature strength, corrosion and wear resistance, and superior stress relaxation behavior. Cu-Ti alloys can be widely used in fabricating elastic components in instruments and meters, relay contacts, lead frames and corrosion and wear resistant materials. However, the mechanism of their decomposition and.coexistence of spinodal decomposition and ordering have not, been clarified; the effects and mechanisms of microalloying elements Co, Cr, V, Mg, etc. has not been profoundly studied; the effects of phase transformation on properties of these alloys are not well known. This project aims to: (i) suppress the decomposition during quenching by addition of the third constituent element in Cu-Ti alloy and then study conveniently the sequence of phase transformation during the early stage of aging. (ii) reveal the feature and the effects of phase transformation on properties of Cu-Ti alloy during aging from the viewpoints of crystallography, thermodynamics and kinetics of phase transformation; (iii) investigate the interactions between solute atoms on the atomic level by three dimensional atom probe and then elucidate the roles and mechanisms of Co, Cr, V, and Mg etc. during aging, (ⅳ) study the strengthening mechanisms and then build the quantitative model of strengthening mechanisms.

在众多Cu-Be的替代合金中，Cu-Ti合金因其更优越的高温强度和抗应力松弛行为以及耐蚀、耐磨性能尤其引人注目。该合金可广泛用于制造精密仪器仪表的弹性元件、继电器、耐磨耐蚀元件、引线框架等。目前，人们对Cu-Ti合金的脱溶机制以及调幅分解和有序化共存的问题仍未予以澄清；对少量或微量元素Co、Cr、V、Mg等合金化的作用机理缺乏深入的研究；对合金中的相变对其性能的影响规律也缺乏清晰的了解。本项目拟通过在Cu-Ti合金中添加第三组元来在抑制淬火过程中调幅分解或有序化反应的发生，从而可以方便地研究合金在时效早期的相变贯序；从晶体学、相变热力学及动力学的角度来揭示时效脱溶过程中的相变特征及其对合金性能的影响；采用三维原子探针技术从原子层面来研究合金时效过程中溶质原子之间的相互作用，从而阐明Co、Cr、V、Mg等合金化元素在时效过程中的作用机理；研究各种强化作用机制，建立各强化机制的定量化模型。

时效强化的稀浓度Cu-Ti合金因其高强度、高弹性、耐蚀、耐磨和抗应力松弛性能而被应用于弹性元件，是理想的Cu-Be合金替代材料。Cu-Ti合金的连续脱溶析出涉及原子的短程有序化、调幅分解、长程有序化等复杂相变过程而成为连续相变的重要合金，但有序化和调幅分解是否存在及其发生的先后顺序一直未能厘清。本项目研究了不同成分合金在不同温度下时效的力学、导电性能变化规律；利用高分辨电镜研究了合金时效时析出相特征，查明了不同温度下的析出贯序；利用三维原子探针研究了不同处理态Cu-Ti合金在固溶淬火、时效过程中溶质原子团簇和析出相的尺寸分布、成分变化规律。得出的重要研究结果如下：.(1)Cu-4.5Ti合金在固溶淬火时就已发生了调幅分解和有序化，时效初期过渡态的1/4{1 1/2 0} 有序化Cu3Ti相连续转变为具有D1a结构的β’-Cu4Ti有序相。此亚稳、共格、有序的棒状β’-Cu4Ti相使合金获得了最大的硬度。而调幅组织和β’-Cu4Ti相在时效的早期对合金的强化贡献巨大。500 ℃2 h时效后，合金能获得290 HV的硬度以及9 %IACS的导电率。.(2)Cu-4Ti-1Al合金400℃1h时效后，其析出贯序如下：过饱和的固溶体→调幅分解→亚稳、共格的β′-Cu4Ti相。Cu-4Ti-1Al合金在600℃1h时效后，晶内以连续析出的β′-Cu4Ti相为主，晶界上有胞状组织（β-Cu4Ti平衡相和α固溶体）出现。二者的位向关系如下：(111)α‖(010)β，[ -101]α‖[501]β。合金650℃1h时效后，析出相以不连续析出的胞状组织为主。Al的加入作用主要有三个：Al起到了固溶强化作用；推迟了有序化的发生；降低了合金的β′-Cu4Ti相共格固溶度线温度。.(3) Cu-4Ti合金在固溶淬火过程中合金发生了一定程度的溶质偏聚现象，而随着时效过程的进行，溶质原子偏聚和团簇尺寸逐渐增大，溶质原子Ti的含量逐渐下降。在101-500个溶质原子的团簇中，Cu/Ti比值接近3:1，相当于Cu3Ti短程有序相。当团簇中溶质原子的尺寸大于500个溶质原子时，此时团簇中Cu/Ti的原子比为4:1，已形成β'-Cu4Ti相。本项目的研究结果不仅对制备高性能的高强高弹导电铜合金具有重要的应用价值，而且大大丰富了固态相变等理论基础，从而推动相关产业的可持续发展。.