Three body wear properties of high chromium cast iron ztap / HCCI composite

Take photos of the worn sample surface, import the pictures into image Pro Plus software, and identify and select the area of ceramic particles by setting the chroma threshold area of ceramic particles, as shown in Figure 1. Then the percentage of ceramic particles in the wear samples was calculated by software, and the volume fraction of ceramic particles in the wear samples was determined to be about 32 vol%.

Figure 2 shows the volume loss comparison of ztap / HCCI composite and HCCI three body wear test. Figure 2 (a) shows the volume loss in a single grinding path. It can be seen that the wear volume loss of ztap / HCCI composite is much less than that of HCCI in a single grinding path, and the volume loss of composite and HCCI decreases gradually with time and finally tends to be stable. The three body wear properties of the composites are more than 3 times of HCCI at the pre and post wear stages. Figure 2 (b) shows the cumulative wear volume loss. At the end of eight grinding cycles, that is, after 480 min of wear time, the accumulated wear volume of ztap / HCCI composite and HCCI is 173.2 mm3 and 757.6 mm3, respectively.

Figure 3 (a) shows the micro wear morphology of the columnar zone of ztap / HCCI composite. For HCCI matrix with columnar zone, because there is no ztap on the surface, the wear resistance phase is all HCCI, so the wear loss of columnar zone is larger than that of composite zone in early wear stage, which is the reason why the wear loss of composite in early stage is more than that in later stage. Compared with HCCI matrix, quartz sand particles are hard phase. In the wear process, the edge angle of the abrasive cuts the HCCI matrix and produces furrow on the surface. The direction of the furrow is basically the same as that of the abrasive cutting. Under pressure, some abrasives are embedded in the matrix and soften the surrounding metal matrix to produce extrusion lip. At the later stage of wear, the wear loss of the columnar zone is lower than that of the composite zone, which mainly supports the composite.

Figure 3 (b) shows the micro wear morphology of ztap / HCCI composite. In the early stage of wear, ztap and HCCI matrix share the wear. Because the hardness of ceramic is much larger than that of matrix, the wear of metal matrix is larger, and ceramic particles gradually protrude from the worn surface. In the middle stage of wear, ceramic particles become the main bearing phase of anti-wear. The metal matrix at the front end of the wear direction is in direct contact with the abrasive and the wear is serious. There is an obvious height difference between the ceramic particles and the metal matrix at the front end, while the wear amount of the metal matrix at the back end is small, forming a slope shape with ceramic particles.

On the one hand, the “shadow effect” is formed due to the protrusion of ceramic particles, which reduces the direct contact between abrasive and metal matrix, as shown in Fig. 3 (c). On the other hand, because the hardness of ZTA ceramic is higher than that of quartz sand abrasive, the abrasive will be broken after contact wear with ceramic particles, and the subsequent grinding effect on metal matrix will be obviously weakened. At this time, the furrow on the surface of matrix mainly appears at the edge of ceramic particles. At the same time, the matrix with weak wear at the back end can support ceramic particles, absorb the cutting stress of some abrasives on ceramic particles, and improve the toughness of ztap. In the late stage of wear, the metal matrix around the ceramic particles is worn too seriously and concave, and the support for ceramic particles is lost. The stress of ceramic particles increases, resulting in contact fatigue and local fatigue spalling. In the actual wear process, due to the uneven distribution of ceramic particles in the composite, the wear cycle exists at the same time, so the wear resistance of the composite tends to be stable after a period of wear.