冷轧退火循环对富镍TiNiZr合金微观组织及力学性能的影响

Microstructure and mechanical properties of Ni-rich TiNiZr alloy associated with repeated cold-rolling and annealing

  • 摘要: TiNi形状记忆合金具有优异的功能特性和结构特性,在多种领域有着明确的目标需求。本文聚焦B2结构奥氏体富镍 TiNi合金,拟通过冷轧退火循环调控TiNi合金微观结构,以期提升合金较低的力学强度和塑性形变能力。系统考察了Ti48.9Ni50.9Zr0.2和Ti47.9Ni51.9Zr0.2合金力学性能和微观结构与冷轧形变以及再结晶退火之间的依赖关系。拉伸力学性能测试表明,冷轧退火循环可显著提升合金综合力学性能,其中Ti48.9Ni50.9Zr0.2合金6道次冷轧退火后抗拉强度从未轧制样品的550 MPa提升至1070 MPa,断后伸长率从4.9%增加至10.0%。通过EBSD、SEM和TEM微观结构观察可以发现,合金多道次冷轧退火后,形变组织和再结晶组织交替变化,合金晶粒显著细化,发生了明显的择优取向,合金织构进一步增强。析出相Ti2Ni和Ti3Ni4破碎细化,纳米级Ti3Ni4与基体间有着良好的晶格匹配性。此外,合金中出现了应力诱发的马氏体以及析出相附近大量高密度位错。合金力学性能与材料微观结构密切相关,强度和塑性提升机制可通过细晶强化、位错强化、沉淀强化和织构强化来理解。

     

    Abstract: TiNi shape memory alloys have clear target demand in a variety of fields owing to their excellent structural and functional properties. In this paper, focusing on B2 structural austenitic Ni-rich TiNi alloys, it is proposed to modulate the microstructure of the TiNi alloys through repeated cold rolling annealing, with an expectation to enhancing the lower mechanical strength and plastic deformation ability of the alloys. The dependence of the mechanical properties and microstructure of Ti48.9Ni50.9Zr0.2 and Ti47.9Ni51.9Zr0.2 alloys on cold rolling deformation and recrystallization annealing was systematically investigated. The tensile mechanical property tests showed that the repeated cold rolling annealing could significantly enhance the overall mechanical properties of the alloys, in which the tensile strength of Ti48.9Ni50.9Zr0.2 alloy is increased from 550 MPa in the unrolled samples to 1070 MPa after 6 passes of cold rolling annealing, and the elongation after fracture has grown from 4.9% to 10.0%. The EBSD, SEM and TEM microstructural observation reveals that the deformation and recrystallization structures of the alloy change alternately after multi-pass cold rolling and annealing, and the alloy grains are significantly refined and undergo an obvious preferred grain orientation. In addition, the basal texture of the alloy is further enhanced. The Ti2Ni and Ti3Ni4 precipitates were broken and refined during cold deformation, in which the nano-sized Ti3Ni4 precipitate exhibits a favorable matching with matrix. Furthermore, stress-induced martensite as well as a large number of high-density dislocations in the vicinity of the precipitation phases appeared in the alloy. The mechanical properties of alloys are strongly related to the microstructure, and the strengthening mechanisms can be understood by grain refinement strengthening, dislocation strengthening, precipitation strengthening and texture strengthening.

     

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