Solid-liquid heat-treatment improving microstructural homogeneity and healing pores/cracks in Ni60A hardfacing layer

Résumé fourni par la source

Ni-Cr-B-Si hardfacing alloys are expected to be used in pumps of nuclear power plants owing to their excellent wear resistance and lower dose rate. Microstructural heterogeneity and pores/cracks are main issues that limit the widespread commercial application. In this work, a solid–liquid heat-treatment (SLHT) post-process that enables improving microstructural homogeneity and completely healing pores/cracks in hot isostatic pressing diffusion bonded (HIP-DBed) Ni60A hardfacing layer is proposed. High temperature confocal microscope-differential thermal analysis (HTCM-DTA) technique is used to perform in-situ observation of the microstructure/pores evolution and to determine SLHT parameters. The obtained SLHT parameters (1000 ℃, holding for 30 min) can completely heal the cracks produced by thermal shock. The mechanisms of pores/cracks healing are proposed based on the in-situ and ex-situ experiments. The effects of the SLHT on mechanical properties and microstructural evolution are also investigated. Although the microhardness, flexural strength and wear resistance, are slightly reduced after the SLHT process, they still maintain relatively high values. Also, the corrosion resistance of the SLHTed hardfacing layer is improved, which may be related to pores healing.