The paper describes mechanical tests of a nanocomposite produced from the ferromagnetic shape memory Fe−Ni−Co−Ti alloy under uniaxial tension over a wide temperature range. The production of the nanocomposite was preceded by preliminary thermomechanical treatment (TMT), involving drawing, quenching, and ageing, for precipitation hardening. The TMT imparted high superelastic strain and shape memory effect to the nanocomposite. The preliminary TMT with strain ψ = = 7.4−22.5% aged at T = 650°C for 5−10 min was experimentally found to correspond to the optimal combination of the maximum superelastic strain and shape memory effect. This contributed to the phase and twinning plastic deformation of the nanocomposite over the test temperature range Ms < Ttest < Af (where Ms is the start temperature of forward martensitic transformation on cooling and Af is the finish temperature of reverse martensitic transformation on heating). A plateau with constant stress was found in the two-phase Mf < Ttest < Ms region on the tensile curve at drawing strain ψ = 22.5%. A significant increase in the preliminary strain (more than 40%) substantially stabilized the austenitic matrix, thus inhibiting the martensitic transformation and reducing reversible effects because the austenite grain size refines when the lattice defect density increases. The austenite grain size distribution was assessed versus the chosen TMT conditions. When the austenite grain size increased, the superelastic strain recovery became higher. The factors leading to greater superelasticity were analyzed within different phenomenological models. The TMT has a crucial role in the variation of structure and mechanical properties, in turn promoting inelastic effects at different temperatures.

中文翻译：

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热机械处理对具有形状记忆效应的 Fe-Ni-Co-Ti 铁磁合金纳米复合材料应变行为的影响

该论文描述了由铁磁形状记忆 Fe-Ni-Co-Ti 合金制成的纳米复合材料在很宽的温度范围内在单轴拉伸下的机械测试。在纳米复合材料的生产之前进行初步热机械处理 (TMT)，包括拉伸、淬火和时效，以进行沉淀硬化。TMT 赋予纳米复合材料高超弹性应变和形状记忆效应。实验发现，应变 ψ = = 7.4-22.5% 在 T = 650°C 下老化 5-10 分钟的初步 TMT 对应于最大超弹性应变和形状记忆效应的最佳组合。这有助于纳米复合材料在测试温度范围内的相和孪晶塑性变形 Ms < Ttest < Af（其中Ms是冷却时马氏体正向转变的开始温度，Af是加热时马氏体逆向转变的结束温度）。在拉伸应变 ψ = 22.5% 时，在拉伸曲线上的两相 Mf < Ttest < Ms 区域发现具有恒定应力的平台。初始应变的显着增加（超过 40%）基本上稳定了奥氏体基体，从而抑制了马氏体转变并降低了可逆效应，因为当晶格缺陷密度增加时奥氏体晶粒细化。奥氏体晶粒尺寸分布与所选的 TMT 条件相比较。当奥氏体晶粒尺寸增加时，超弹性应变恢复率变得更高。在不同的现象学模型中分析了导致更大超弹性的因素。TMT在结构和机械性能的变化中起着至关重要的作用，反过来又促进了不同温度下的非弹性效应。