摩擦学用新型富镍镍钛铪合金的热处理-显微组织-硬度关系
Heat treatment - microstructure - hardness relationships of new nickel-rich nickel-titanium-hafnium alloys developed for tribological applications
摘要：
研究了各种热处理对新型Ni 56 Ti41 Hf 3和Ni 56 Ti 36 Hf 8（原子%）合金的显微组织和硬度的影响，以评价这些材料在摩擦学应用中的适用性。对于固溶退火（SA）的Ni 56 Ti 36 Hf 8合金（716 HV），观察到由于Hf原子的固溶强化效应，导致与含有54体积% Hf的Ni 56 Ti 41 Hf 3合金相当的硬度。Ni_4Ti_3析出相的硬度为707 HV。在Ni 56 Ti41 Hf 3合金中，在300 ℃时效12 h后达到的最大硬度（752 HV）归因于致密的、半共格的Ni 4 Ti 3相的析出。不同于透镜状形态通常观察到的二元NiTi合金，块状Ni 4 Ti 3的形态内形成Ni 56 Ti 36 Hf 3由于在沉淀物/基体界面处的惯习平面的垂直方向上的较小的晶格失配。Ni 56 Ti 36 Hf 8合金在300 ℃时效12 h后再进行550 ℃时效4 h，硬度最高，达到769 HV。这种两步时效处理诱导两种散布的沉淀相（即H相和新的立方富Ni沉淀相）的密集纳米级沉淀，导致该家族合金表现出的最高硬度。使用原子探针层析术测量立方富Ni沉淀物的组成为约Ni61.5Ti31Hf7.5，而HAADF-STEM揭示了54个原子基序的立方结构（α = 8.87埃），并且电子衍射显示该结构属于pm-3 m（No.221）空间群。
英文摘要：
The effects of various heat treatments on the microstructure and hardness of new Ni56Ti41Hf3 and Ni56Ti36Hf8 (atomic %) alloys were studied to evaluate the suitability of these materials for tribological applications. A solid-solution strengthening effect due to Hf atoms was observed for the solution annealed (SA) Ni56Ti36Hf8 alloy (716 HV), resulting in a comparable hardness to the Ni56Ti41Hf3 alloy containing 54 vol.% of Ni4Ti3 precipitates (707 HV). In the Ni56Ti41Hf3 alloy, the maximum hardness (752 HV), achieved after aging at 300C for 12 h, was attributed to dense, semi-coherent precipitation of the Ni4Ti3 phase. Unlike the lenticular morphology usually observed within binary NiTi alloys, a blocky Ni4Ti3 morphology formed within Ni56Ti36Hf3 due to a smaller lattice mismatch in the direction normal to the habit plane at the precipitate/matrix interface. The maximum hardness for Ni56Ti36Hf8 (769 HV) was obtained after applying an intermediate aging step (300C for 12 h) followed by normal aging (550C for 4 h). This two-step aging treatment induces dense nanoscale precipitation of two interspersed precipitate phases, namely H-phase and a new cubic Ni-rich precipitate phase, resulting in the highest hardness exhibited yet by this family alloys. The composition of cubic Ni-rich precipitates was measured using atom probe tomography to be approximately Ni61.5Ti31Hf7.5, while HAADF-STEM revealed a 54 atom motif cubic structure (a= 8.87 Angstroms), and electron diffraction showed that the structure belongs to the pm-3m (No. 221) space group.
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