Effect of Cryogenic Duration on the Tribological Properties of Sintered Polycrystalline c-BN During Sliding Mating Materials in Vacuum

Abstract

The service performance of polycrystalline cubic boron nitride (PcBN) tools undergoes significant changes due to the deep space environment to the structure and wear behaviors of PcBN. In this paper, the effect of cryogenic treatment (CT) was studied to investigate the physical and tribological behaviors of PcBN. The hardness and wear resistance of PcBN are improved but wear forms are not affected, which are abrasive wear. The shedding of cBN played the role of micro-cutting edges, carving furrows on surfaces. As the CT duration increases, the wear rate of PcBN decreases from 2.56×10-8 mm3/N mm to 1.61×10-8 mm3/N mm for sliding against Si3N4. When PcBN slid Al2O3, the lowest wear rate is 1×10-8 mm3/N mm which the decline reached 34%. Due to discrepancies in physical and mechanical properties, Si3N4 and YG8 balls exhibit abrasive and adhesive wear, and Al2O3 shows fatigue wear. Until the fatigue failure appeared, Al2O3 exhibited the lowest wear rate of 2.30×10-9 mm3/N mm. Among three materials, the wear rate of Si3N4 was the highest. By calculating the wear rate ratio of the materials, it was concluded that the optimal removal efficiency was achieved for Si3N4 and YG8 when CT duration is 24 and 48 hours, respectively.