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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 Si 3 N 4. When PcBN slid Al 2 O 3 , the lowest wear rate is 1 × 10−8 mm3/N mm which the decline reached 34 %. Due to discrepancies in physical and mechanical properties, Si 3 N 4 and YG8 balls exhibit abrasive and adhesive wear, and Al 2 O 3 shows fatigue wear. Until the fatigue failure appeared, Al 2 O 3 exhibited the lowest wear rate of 2.30 × 10−9 mm3/N mm. Among three materials, the wear rate of Si 3 N 4 was the highest. By calculating the wear rate ratio of the materials, it was concluded that the optimal removal efficiency was achieved for Si 3 N 4 and YG8 when CT duration is 24 and 48 h, respectively. [ABSTRACT FROM AUTHOR]

Tribological properties are the significant factors to evaluate the application of polycrystalline cubic boron nitride(PcBN) with hard materials in vacuum conditions. In the current paper, the tribological properties of PcBN and WC-Co cemented carbide (YG8) during the sliding process are carried out under different loads in vacuum by ball-disk friction and wear experiments. The wear tracks of PcBN and wear scars of YG8 were characterized. The results show that the wear mechanisms of PcBN in vacuum are mainly abrasive wear and adhesive wear. Furthermore, furrows are also detected on the surface of YG8 balls due to the plowing of exfoliated cubic boron nitride. As a result, abrasive wear is the failure form of YG8 ball. The average CoF is negatively correlated with the loads. Moreover, the relationship between friction and wear is discussed deeply. The wear rate of YG8 ball is positively correlated with the load. Additionally, the wear rate ratio of PcBN and YG8 indicates that higher loads can promote the wear rate of YG8, but it also leads to the rapid wear of PcBN. The results could provide significant instructions for the regulation and control of the tribological properties of PcBN in the coming outer space exploration activities. [ABSTRACT FROM AUTHOR]

In order to understand the surface and interface conditions of polycrystalline cubic boron nitride (PcBN) sliding against bearing steel in vacuum environments, the effects of different loads on the tribological behaviors of PcBN and bearing steel AISI 52100 were studied deeply in a vacuum tribometer. Furthermore, the wear tracks of PcBN and the wear scars of AISI 52100 were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the stable coefficient of friction (CoF) of the tribopair experiences a decrease first and then an increase with the increase in loads from 2 N to 15 N. The adhesive layer increases with the increase in loads, and the formation of adhesive layer contributes to the change of CoF and wear rate of counterpart balls. The adhesive layer is formed due to the combination of high contact stress and high temperature. Meanwhile, the exfoliated cubic boron nitride grains are embedded into the adhesive layer as abrasive grains, resulting in abrasive wear. Thus, the main wear mechanisms are adhesive wear and abrasive wear. [ABSTRACT FROM AUTHOR]

In order to understand the thermal damage mechanisms of polycrystalline cubic boron nitride (PcBN) under elevated temperature and the following influences on its tribological behaviors, the physicochemical characteristic of annealed PcBN under various temperatures was investigated by X-ray diffraction, Scanning electron microscopy and energy dispersive x-ray spectroscopy measurements. Furthermore, the tribological behaviors of annealed PcBN sliding against the typical commercial AISI 52100 steel ball were evaluated. These results demonstrate that the new oxidation phase TiO 2 , which exhibits uniform whisker with nanorod shape owing to the effect of gas diffusion channels, is produced from the binder phases TiN and TiB 2 above 800 °C. Moreover, the coefficient of friction (CoF) dependent on annealed temperatures is coincident with the changing tendency of wear volume of counter balls, where the CoF and wear volume bottomed at 800 °C. Below 800 °C, the wear mechanism is adhesive wear owing to the formation of the iron transfer film, while at 900 °C is abrasive wear because of the spalling off of grains acting as the three-body hard phases. [ABSTRACT FROM AUTHOR]

Polycrystalline cubic boron nitride (PcBN) is a widely used tool material for cutting hard materials under high-speed and heavy-duty cutting conditions. As the need for in-orbit manufacturing and service in vacuum environment of outer space grows, understanding the tribological behavior of PcBN tools during vacuum operation becomes increasingly important. This study investigates the effect of different working conditions on the tribological behavior of PcBN discs and high‑carbon chromium alloy steel (440c) balls in vacuum. The tribological behavior of tribopair is analyzed. The experimental results reveal that the average of coefficient of the friction (CoF) is generally lower at 100 r/min than at 300 r/min and decrease with increasing load at two different speeds. The CoF of the 300 r/min group exhibits greater ups and downs at different load cases. The wear rate increases and then decreases with increasing load at different speeds. These fluctuations in CoF and wear rate are attributed to the transformation of the wear form and the effect of frictional heat build-up. Based on the SEM and EDX results, the wear mechanism is predominated by abrasive wear, gradually transitioning to adhesive wear with increasing loads. These findings provide insights into the tribological behavior of PcBN composite materials in vacuum. The results aim to inform the development of more efficient and dependable PcBN tools for in-orbit manufacturing and service applications. • The tribological behaviors of PcBN/440c was investigated in vacuum. • The wear mechanism exhibits a combination of abrasive and adhesive wear. • The contact stress growth drives the wear mechanism transformation process. • The increase of rotational speed accelerates the transformation process. • Working conditions affect CoFs and wear rates in different ways. [ABSTRACT FROM AUTHOR]