We investigate systematically four outbursts of black hole system GX 339-4 observed by the Rossi X-ray Timing Explorer (RXTE) in both spectral and timing domains and find that these outbursts have some common properties, although they experience different ‘q’ tracks in the hardness–intensity diagram (HID). While the spectral indices are around 1.5 in the low/hard state (LHS) and 2.4 in the soft intermediate state (SIMS) and high/soft state (HSS), the spectral parameters of thermal, non-thermal, and reflection components vary significantly in transitions from the LHS to HIMS. Also, the quasi-periodic oscillation (QPO) shows a peculiar behaviour during the state transition between the LHS and HIMS: the RMS drop of the type C fundamental QPO is accompanied by the appearance of the second harmonic. Interestingly, the QPO RMS is found to have a similar linear relationship with the non-thermal fraction of emission in different outbursts. These findings provide more clues to aid our understanding of the outbursts of a black hole X-ray binary system.

The WC-Co composite coating was prepared on SS 316L by plasma arc welding technology. The microstructure, phase composition, and microhardness of the WC-Co composite coating were thoroughly studied. The corrosion behaviour including electrochemical corrosion, cavitation erosion, and erosion corrosion was tested. The results showed that the WC-Co coating exhibited a good metallurgical bond with the substrate. The average microhardness of the WC-Co coating reached 1785 HV, which was 9.4 times that of the SS 316L. The corrosion current density of the WC-Co composite coating was one order of magnitude lower than that of the substrate. Meanwhile, the cumulative mass loss of cavitation erosion and erosion corrosion of the WC-Co composite coating was much lower than that of the SS 316L.

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