Abstract

The formation of a liquid phase in titanium nickelide–based alloys, which are enriched in nickel (55.8–55.9 wt %) and abundant in Ti₂Ni/Ti₄Ni₂O_x phase intermetallic particles, is studied. The phase transformations in the alloys are investigated during heating in argon and helium atmospheres in a temperature range of 900–1200°C by differential thermal analysis. The cause for the formation of liquid in the alloys in a gas medium is found to be their oxidation. Oxidation results in the redistribution of the main chemical elements of the alloy on its surface and the formation of titanium- and nickel-rich phases. This leads to the eutectic transformation TiNi + TiNi₃ → L. On heating in a vacuum, the formation of liquid is possible only in the alloy characterized by a high volume fraction of Ti₂Ni/Ti₄Ni₂O_x phase particles. The precipitation of the particles during melting of the alloy depletes its matrix of titanium; this leads to a substantial increase in the nickel content in the matrix as compared to the total nickel content in the alloy. This effect, likely in combination with oxidation, also initiates the eutectic reaction in heating. Liquid-phase (supersolidus) sintering is shown to be possible for titanium nickelide–based alloys due to the eutectic reaction.

中文翻译：

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钛镍基合金的相组成对烧结过程中液体形成的影响

摘要

研究了镍镍钛基合金中液相的形成，该合金富含镍（55.8-55.9 wt％），并富含Ti ₂ Ni / Ti ₄ Ni ₂ O _x相金属间化合物。通过差热分析，研究了在900-1200°C温度范围内的氩气和氦气气氛中加热期间合金中的相变。发现在气体介质中的合金中形成液体的原因是它们的氧化。氧化导致合金的主要化学元素在其表面上重新分布，并形成富含钛和镍的相。这导致了TiNi + TiNi ₃ → L的共晶转变。在真空中加热时，仅在以高体积分数的Ti ₂ Ni / Ti ₄ Ni ₂ O _x相颗粒为特征的合金中才可能形成液体。在合金熔化过程中，颗粒的沉淀耗尽了其钛基。与合金中的总镍含量相比，这导致基体中镍含量的大幅增加。这种作用，可能与氧化作用结合，也会引发加热中的共晶反应。由于共晶反应，液相烧结（超固相线）对于镍钛合金是可行的。