纳米级90W-7Ni-3Fe复合粉末的低温烧结机制

Low-Temperature Sintering Mechanism of Nanometer 90W-7Ni-3Fe Composite Powder

采用DTA研究了喷雾干燥-H2还原法制备的纳米级90W-7Ni-3Fe复合粉末随温度升高时熔点和相的变化,依此为根据研究了试样在不同烧结温度和不同烧结时间下的烧结特性。采用扫描电子显微镜和金相仪分别对试样断口进行了形貌观察和W晶粒测试,并对烧结样的性能进行了测定与分析。研究结果表明:保温时间为120min时,随着烧结温度的提高,试样的性能有显著的变化,当烧结温度为1390℃时,试样的抗拉强度、延伸率和相对密度都达到一个极大值,分别为888.3MPa,12.9%和99.0%;当烧结温度为1390℃时,随烧结时间的延长,试样的性能也有显著的变化,试样的抗拉强度、延伸率和相对密度在保温120min时都达到一个极大值;平均W晶粒度为20μm,W晶粒呈球形或近球形;复合粉末烧结活性高,比传统烧结温度降低80℃;粉末中高的氧含量和在干氢中的烧结,使得试样在液相烧结时容易出现孔洞和气泡,W晶粒和粘结相分布不均匀,致使试样力学性能偏低。

Melting point and phase changes of nanometer 90W-7Ni-3Fe composite powder synthesized by spray drying-H2 reduction method were measured by DTA. On the basis of the results, sintering characteristic of samples were studied at different sintering temperature and time. Fracture morphology and W crystal sizes of samples were measured by SEM and optical morphology, respectively. Relative density, tensile strength and elongation of samples were also measured and analyzed. The result shows that when sintering time is 120 minutes, properties of samples change evidently with the increase of sintering temperature. Relative density, tensile strength and elongation of samples reach the maximums, and are 99.0%, 888.3 MPa, 12.9% at 1390℃, respectively. When sintering temperature is 1390℃, properties of samples change evidently with the increase of sintering time. Relative density, tensile strength and elongation of samples arrive at the maximums when holding for 120 minutes, too. Average W crystal sizes are 20 μ m and W crystal morphology are spherical or nearly spherical. Sintering temperature is 80℃ lower than conventional sintering because of higher sinterability of composite powder. Mechanical properties is little low because of appearance of cavities and vapour at liquid sintering.