W-Mo-Ni-Fe重合金金属间化合物相析出机制研究

Precipitation mechanisms of intermetallic compounds in W-Mo-Ni-Fe heavy alloys

为了分析Mo元素含量对液相烧结W Ni Fe重合金显微组织的影响和探讨Mo元素含量与基地相、析出相等各相组成的关系 ,以及了解合金于炉冷后在固相与基地相接口析出的金属间化合物相之形成机制 ,本研究使用具有相同基地相组成但不同Mo元素含量 (Mo的原子数分数为 15 %～ 5 9% )的试片 ,以SEM、EMPA观察显微组织的变化 ,并使用XRD对金属间化合物析出相进行结构分析与鉴定 ,最后再以DTA热分析仪器量测合金的相变化温度 ,以厘清金属间化合物相的析出机制。试验结果显示 ,当合金中含有高比例的Mo元素时 ,烧结后在基地相中固溶的Mo元素与W +Mo元素总和将随之升高 ,除了造成基地相的凝固温度下降以外 ,也形成大量的 (W ,Mo) 0.5-x(Ni,Fe) 0.5+x(x =0～ 0.0 4 )金属间化合物析出相 ,而此金属间化合物相中 ,Mo元素所占的比例会随着添加的Mo元素比例增加而呈线性上升。热分析结果显示 ,金属间化合物相的析出温度大约是在 1349～ 135 5℃之间 ,而基地相的凝固温度则从 14 15℃降低到 1336℃。根据这些现象可以了解 ,金属间化合物相的形成机制与合金成分中的MMo/ (MW +MMo)比值有关 ,当比值高于 0.6 6时 ,金属间化合物相的析出机制为偏晶反应 (monotecticreaction) ;当比值在 0.5～ 0.6 6之间时 ,析出机制是属于共晶反?

In order to investigate the effect of Mo on the microstructural evolution of W-Ni-Fe heavy alloys, phase composition, and precipitation mechanism of intermetallic compound, alloys with binder matrixes of the same composition but different ratios of W to Mo (Mo: 15at%-59at% ) were liquid phase sintered. The analysis of phases was carried out using SEM, EPMA, XRD, and DTA. Results indicated that the increased concentration of Mo in the matrix, as a result of increased ratio of Mo in the alloy, not only reduced the solidification temperature of the matrix phase from 1415°C to 1336°C, but also promoted the formation of intermetallic (W,Mo)0.5-x(Ni,Fe)0.5+x, (x = 0-0.04) compound. The atomic ratio of Mo in this intermetallic compound was found to increase linearly with the atomic ratio of Mo in the alloy, but the precipitation temperature of this intermetallic compound was very consistent, ranging from 1349°C to 1355°C. Due to such varying phase transformation temperatures, the phase transformation temperature of the intermetallic compound was determined by the atomic ratio of Mo to Mo and W (MMo/Mw + MMo) in the alloy. It is a monoeutectic reaction when this ratio is higher than 0.66, or eutectic reaction when this ratio ranges between 0.5 and 0.66. When this ratio is between 0.34 and 0.5, the precipitation of the intermetallic compound is either eutectoid or peritectoid. No intermetallic compound was found for a ratio lower than 0.2.