论文标题
无粘合钨碳化物的低温蠕变具有不同的谷物尺寸
Low-temperature creep of binderless tungsten carbide with different grain sizes
论文作者
论文摘要
已经研究了具有不同晶粒尺寸的碳化钨的压缩测试中的蠕变机制。来自纳米，亚微米和微米级WC粉末的SPS获得了高密度（96.1-99.2％）的WC样品（96.1-99.2％）。样品的厚度为〜0.3 mm的粗粒（CG）表面层，超颗粒（UFG）的中央部分由WC组成，其中少数W2C。蠕变测试是在两个方案中进行的：（模式＃1）在不同温度（1300-1375C）以70 MPa保持； （模式＃2）在1325c的不同应力（50、70、90 MPa）下进行测试。在模式＃1中进行测试以确定有效的蠕变激活能量QCR，而模式＃2的测试 - 确定功率定律蠕变方程中的系数n。发现W2C颗粒的分数从1.7增加到4％的增加，导致QCR从17.5下降到13 ktm。系数n等于3.1-3.7。从纳米植物烧结的WC中的QCR显示为31 ktm。该值比商业粉末SPS获得的UFG样品中的QCR高1.5-2倍。当烧结纳米植物以吸附的氧气浓度增加时，W2C的分数增加被认为是测试UFG样品时QCR增加的起源之一。证明从碳化钨样品表面的CG层的机械去除可导致加速蠕变，QCR和系数n至2.5-2.6的降低不足。建议样品的蠕变速率通过CG表面层中的蠕变过程和样品中心部分中的蠕变过程同时确定。表面CG层中的蠕变速率取决于WC晶格中碳扩散的强度，而UFG中心部分的蠕变速率是通过晶界扩散的强度。
The creep mechanism in the compression testing of the tungsten carbide with different grain sizes has been studied. The WC samples with high density (96.1-99.2%) were obtained by SPS from nano-, submicron, and micron-grade WC powders. The samples had a coarse-grained (CG) surface layers of ~0.3 mm in thickness and ultrafine-grained (UFG) central parts consisting of WC with a small fraction of W2C. The creep tests were conducted in two regimes: (Mode #1) holding at different temperatures (1300-1375C) at 70 MPa; (Mode #2) tests at different stresses (50, 70, 90 MPa) at 1325C. Tests in Mode #1 were done to determine the effective creep activation energy Qcr while tests in Mode #2 - to determine the coefficient n in the power law creep equation. The increasing of the fraction of the W2C particles from 1.7 up to 4% was found to result in a decrease in the Qcr from 17.5 down to 13 kTm. The coefficient n equals to 3.1-3.7. The Qcr in the WC sintered from nanopowders was shown to be 31 kTm. This value is 1.5-2 times greater than the Qcr in the UFG samples obtained by SPS from commercial powders. The increased fraction of the W2C formed when sintering the nanopowders with increased adsorbed oxygen concentration was suggested to be one of the origins of the increase in the Qcr when testing the UFG samples. The mechanical removing of the CG layers from the surfaces of the tungsten carbide sample was shown to result in an accelerated creep, insufficient decrease in the Qcr and coefficient n to 2.5-2.6. The creep rate of the samples was suggested to be determined simultaneously by the creep process in the CG surface layers and the creep process in the UFG central parts of the samples. The creep rate in the surface CG layers is determined by intensity of carbon diffusion in the WC crystal lattice while the creep rate in the UFG central parts - by the intensity of grain boundary diffusion.
