Abstract: Thermal fatigue test of two kinds of WC steel bonded carbides with different WC contents was examined on self-strained thermal fatigue testing machines, and thermal fatigue crack propagation process was investigated by optical microscopy and SEM. The results show that a kind of trapezoid crack forms not only on the surface but also in the alloy, and the forming process of this kind of crack is the propagation process of the thermal fatigue crack that forms at the sample notch. Steel matrix prevents the crack from propagating, and WC hard phase induces the crack to propagate. The comprehensive effects of these two factors make thermal fatigue crack form trapezoid crack shape .It is pointed out by analyzing that making WC particles distribute uniformly in the steel matrix and increasing thermal fatigue resistance of the matrix to prevent trapezoid crack from forming are effective methods to increase the thermal fatigue resistance of WC steel bonded carbides.
Formation mechanism of trapezoid crack in WC steel bonded carbide under action of thermal stress
Abstract:
Thermal fatigue test of two kinds of WC steel bonded carbides with different WC contents was examined on self-strained thermal fatigue testing machines, and thermal fatigue crack propagation process was investigated by optical microscopy and SEM. The results show that a kind of trapezoid crack forms not only on the surface but also in the alloy, and the forming process of this kind of crack is the propagation process of the thermal fatigue crack that forms at the sample notch. Steel matrix prevents the crack from propagating, and WC hard phase induces the crack to propagate. The comprehensive effects of these two factors make thermal fatigue crack form trapezoid crack shape .It is pointed out by analyzing that making WC particles distribute uniformly in the steel matrix and increasing thermal fatigue resistance of the matrix to prevent trapezoid crack from forming are effective methods to increase the thermal fatigue resistance of WC steel bonded carbides.
Fig.2 Optical microstructures of specimens; (a)—Sample GJW50; (b)—Sample GJW35
图3 试样表面形成的梯形裂纹形貌(经50次热循环)
Fig.3 Morphologies of “trapezoid crack ” formed on surface of sample(NCycle=50) (a)—Sample GJw50(Not corroded) (b)—Sample GJW35(Corroded by 4% nitric acid alcohol )
图4 加宽的梯形裂纹
Fig.4 Morphology of widening trapezoid crack (Sample GJW35, No.1)
图5 疲劳断口上的梯形裂纹(经500次热循环)
Fig.5 Morphology of trapezoid crack on thermal fatigue fracture surface (NCycle=500, sample GJW50)