At elevated temperatures, the material behaviour of WC-Co hardmetals shows differences under similar loading conditions depending on WC grain size and Co-content. Variations in the chemical composition and microstructure in hardmetals cause different material properties such as strength or creep resistance. In the current work, the influence of WC grain size on creep mechanism and creep resistance was investigated for WC-12 wt% Co hardmetals with 0.4 μm, 0.7 μm and 2.0 μm average WC grain size. Specimens were tested in uniaxial tensile and compression step-loading creep tests at 700 °C and 800 °C under vacuum conditions. Time-dependent creep behaviour with steady-state secondary creep was observed for all hardmetal grades investigated, with specimens creeping faster under tensile than under compressive loading. At 700 °C, the medium-grained hardmetal grade exhibited the highest minimal creep rates ${\dot{\epsilon }}_{\min }$ compared to the submicron and ultrafine-grained grades. In contrast, the ultrafine-grained hardmetal grade showed higher ${\dot{\epsilon }}_{\min }$ at low stresses and 800 °C, because of the high amount of grain boundary area per unit volume, which is advantageous for vacancy diffusion at grain boundaries. Therefore, the ${\dot{\epsilon }}_{\min }$ of the medium-grained hardmetal grade was less affected by temperature than that of the finer-grained grade. Also two stress exponent n-ranges were observed at 700 °C and 800 °C: At low stress levels, n was in the range of about 1. Above a critical stress level, n reached values between about 4 and 6. Beside the influence of the WC grain size on the creep mechanism and creep resistance, damage evolution with increasing stress levels was analysed for the ultrafine-grained grade at 800 °C. The microstructures of three compression step-loading creep tested specimens were examined after maximum stress levels of −350 MPa, −950 MPa and −1350 MPa. Microstructural investigations performed via scanning electron microscopy showed that more and larger cavities had formed at WC/WC interfaces and WC/Co phase boundaries in the specimen tested up to −1350 MPa compared to the ones tested up to −350 MPa and −950 MPa.

在升高的温度下，WC-Co 硬质合金的材料行为在类似的加载条件下显示出差异，具体取决于 WC 晶粒尺寸和 Co 含量。硬质合金中化学成分和微观结构的变化会导致不同的材料特性，例如强度或抗蠕变性。在目前的工作中，研究了 WC 晶粒尺寸对平均 WC 晶粒尺寸为 0.4 μm、0.7 μm 和 2.0 μm 的 WC-12 wt% Co 硬质合金的蠕变机制和抗蠕变性的影响。样品在真空条件下在 700 °C 和 800 °C 下进行单轴拉伸和压缩阶跃加载蠕变试验。对于所研究的所有硬质合金牌号，观察到具有稳态二次蠕变的时间相关蠕变行为，试样在拉伸载荷下比在压缩载荷下蠕变更快。在 700 °C 时，${\dot{\epsilon }}_{\mathrm{分钟}}$与亚微米级和超细粒度级相比。相比之下，超细晶硬质合金牌号表现出更高的${\dot{\epsilon }}_{\mathrm{分钟}}$在低应力和 800 °C 下，由于每单位体积的晶界面积很大，这有利于晶界处的空位扩散。因此，该${\dot{\epsilon }}_{\mathrm{分钟}}$与细晶粒牌号相比，中晶粒硬质合金牌号受温度的影响较小。在 700 °C 和 800 °C 下还观察到两个应力指数n范围：在低应力水平下，n在大约 1 的范围内。高于临界应力水平，n达到约 4 和 6 之间的值。除了 WC 晶粒尺寸对蠕变机制和蠕变抗力的影响外，还分析了 800°C 下超细晶粒等级随应力水平增加的损伤演变。在 -350 MPa、-950 MPa 和 -1350 MPa 的最大应力水平后，检查了三个压缩阶跃加载蠕变测试试样的微观结构。通过扫描电子显微镜进行的微观结构研究表明，与高达 -350 MPa 和 -950 MPa 的测试相比，在测试高达 -1350 MPa 的试样中，在 WC/WC 界面和 WC/Co 相边界处形成了更多更大的空腔。