Study On Contact Fatigue Performance And Fatigue Damage Mechanism Of Coatings Prepared By Supersonic Plasma Spraying

The aim of this paper was to address the contact fatigue performance and fatigue damage mechanism of NiCrBSi and NiCr/Cr₃C₂ coatings prepared by supersonic plasma spraying. The NiCrBSi alloy coating and The NiCr-Cr₃C₂ metal-ceramic coating were deposited on steel (AISI 1045) substrates using supersonic plasma spraying technique; Scanning electronic microscope (SEM), X-ray stress determinator, micro-hardness instrument and nano-indentation tester were used to investigate the morphologies, the residual stress, micro-hardness and mechanical properties of the coatings, respectively; The porosity of coating was measured with Gray-Law; Rolling contact fatigue (RCF) life of the coating was investigated using a ball-on-disc tester; Weibull distribution failure probability map and accelerated life mode were use to characterize the RCF life of coatings. The typical fatigue failure modes of coating were summarized, failure mechanism was discussed as well.The results showed that: (1) Micro-defects in the coating were mainly composed of micro-pores and micro-cracks. The failure modes of coating were mainly spalling failure when content of micro-defects in coating was low. Interfacial delimitation failure became the major failure mode when coating contained more micro-defects and lower bond strength. Probability of surface abrasion failure increased when the pore size of coating was large. (2) The Fan-Montfort hypothesis testing was used to prove that the RCF life of coating accords with Weibull distribution. Map of Weibull distribution failure probability was plotted as well. And the failure probability of random cycle was achieved by this Weibull plot under identical work condition. (3) Accelerated fatigue life model of NiCr-Cr₃C₂ coating was obtaine. And the RCF life of coating under different loads can be predicted using this mode. (4) The stress rose slowly in the first half of fatigue process while increased sharply in the following procedure that made the mid-stage became the critical point of fatigue failure process. (5) Contact fatigue failure modes of coatings include: surface abrasion failure, spalling failure, interfacial delimitation and pitting failure. The surface abrasion failure is associated with the micro-sliding wear between contact piece and coating; the spalling failure is associated with surface and subsurface's micro-defects such as micropores and microfissures; the interfacial delimitation failure is influenced by the deficient strength of coating and substrate, the pitting failure is associated with the no-melt particles and the micro-defects such as micro-porosity in coating surface. (6) The bonding strength between coatings and substrates were obviously enhanced, the coatings' density was improved, at the same time the main failure modes of NiCrBSi coating was changed from interfacial delamination failure to spalling failure by the remelting process. In addition, the contact fatigue life was evidently enhanced after remelting with the distribution much more concentrated.