Three dimensional wear, also known as impact surface wear, mainly describes the wear mechanism on the three body impact abrasive wear surface. At this time, the wear situation is intense, which does not only occur on a two-dimensional plane, so it is expressed in three-dimensional wear.
The wear surface of the sample after three body impact abrasive wear test was observed by SEM. Fig. 1 shows the wear surface of bainitic Martian multiphase wear-resistant cast steel, indicating that strain fatigue, cracks, furrows, embedded abrasive particles and extrusion accumulation are the main wear mechanisms of bainitic Martian multiphase wear-resistant cast steel. The strain fatigue in Figure 1a is caused by fatigue wear and fatigue cracks caused by the contact of different friction bodies. Its morphology is river like, which is highly consistent with the experimental conditions of three body impact abrasive wear. Material exchange often occurs between abrasive and experimental steel, and the embedded abrasive shown in Fig. 1b is one of the most important manifestations. It can be observed from Fig. 1C that there is a spray like structure at the end of the furrow, which is formed by the metal matrix subjected to ploughing and pushing after the furrow is generated. It is named furrow spray. On the end face of the furrow spray, it often exists by extrusion.
Fig. 2a is a schematic diagram of embedded abrasive particles in bainitic Martian multiphase wear-resistant cast steel. The abrasive particles are impacted (step 1) and crushed by the upper sample and the lower sample (step 2). Then, with the impact of the upper sample and the rotation of the lower sample, most of the abrasive flies away from the friction area, and a small part of debris with appropriate shape is screened (step 3) and embedded into the wear surface of the experimental steel (step 4). Fig. 2B illustrates the process of delamination. Strong shear stress and tensile stress promote the initiation, growth and accumulation of microcracks on the wear surface. Cracks tend to cause delamination, which is one of the most harmful failure modes in the wear process. The embedded abrasive particles in the sample of bainitic Martian multiphase wear-resistant cast steel will hinder the crack propagation because it has high yield strength, which firmly binds the abrasive to the surface of the metal matrix and reduces the stress concentration. Furrow is a typical wear mechanism, and it is also an important wear form that can cause wear loss. Fig. 2C shows the mechanism of furrow moving slowly and blocked in bainite Martian multiphase wear-resistant cast steel. The embedded abrasive particles embedded in the sample pass through the surface of the experimental steel and leave a furrow. The ploughed part of the metal matrix is lost in the form of loss of wear, while the other part moves slowly along the surface until it is blocked by reef embedded abrasive particles. The embedded abrasive particles embedded in the sample pass through the surface of the experimental steel and leave a furrow. Part of the metal matrix ploughed out is lost in the form of loss of wear, while the other part moves slowly along the surface until it is blocked by reef embedded abrasive particles. At this time, the metal matrix stops moving and forms furrow spray. The front metal matrix squeezes between the rear metal matrix and abrasive, so a characteristic wear mechanism called extrusion accumulation is formed.
Fig. 3 is a SEM photograph of the three body impact abrasive wear surface of mnl3cr2. It can be seen that the wear surface of mnl3cr2 is similar to the experimental steel, but there are different wear behaviors. The main wear-resistant mechanisms are summarized as embedded abrasive particles, furrow, strain fatigue, cutting, extrusion accumulation and peeling pits.
Fig. 3 is a schematic diagram of the wear mechanism of mnl3cr2 steel. Fig. 3A describes the press in abrasive mechanism of mnl3cr2 steel. Since the yield strength of mnl3cr2 experimental steel is much lower than that of bainite Martian multiphase wear-resistant cast steel, the press in abrasive in mnl3cr2 can not be firmly fixed on the surface and is easier to fall off. In addition, the larger abrasive accepted in the screening step will be pressed deeper in the metal matrix, and the larger peeling pit generated after the separation of this part of the abrasive will cause greater damage to mnl3cr2. Fig. 3B shows the mechanism of furrow movement and obstruction in mnl3cr2. Due to its low yield strength and initial hardness, mnl3cr2 is easier to be plowed by the press in abrasive embedded in the sample, and more metal substrates are plowed out of the surface and pushed. These plowed metal substrates are doped with abrasive and abrasive particles and extruded and accumulated, and the embedded abrasive particles are not firmly fixed in the surface of mnl3cr2, Therefore, the continuous movement of furrow spray is easier to be prevented by extrusion and accumulation. At this time, furrow spray forms larger protrusions on the wear surface, and then the high protrusions are cut off by strong pressure. This wear behavior is called cutting. To provide evidence of this mechanism, furrows in SEM images were measured. The results show that the average length of 29 furrows in Bei Ma multiphase wear-resistant cast steel is 91 PM, while the average length of 35 furrows in mnl3cr2 is 49 PM. The data in the sample show that the furrow in mnl3cr2 is shorter and deeper than that in bainite Martian multiphase wear-resistant cast steel. Fig. 3C is a schematic diagram of spalling pit. The stronger work hardening in mnl3cr2 leads to a greater hardness change between the hardened area and the initial area (the average hardness of mnl3cr2 is increased by 342hv, while the average hardness of bainitic Martian multiphase wear-resistant cast steel is increased by 240hv), which is conducive to microcrack initiation. Therefore, microcracks in mnl3cr2 are initiated below the wear surface rather than on the wear surface. Then, the microcracks grow and converge into larger cracks. After that, the crack grows to the wear surface and leads to large delamination and spalling. Finally, the spalling pit exposes the initial area with low hardness, and the abrasive and abrasive particles tend to embed and gather in the spalling pit with low hardness.