Research On Ni/TiC Coating On Aluminum Alloy Die Casting Die Surface By SHS

The aluminum alloy die-casting die,working in a harsh condition,is easy to be failured because of the aluminum corrosion and cyclic thermal stress.It is of great significance to study the surface treatment technology in order to improve the service life of aluminum alloy die-casting die with its outputs and requirements increasing.In this paper,the millimeter-level Ni/TiC functionally gradient cermet layer was prepared on H13 steel surface by self-propagating high-temperature synthesis and pseudo hot isostatic pressing?SHS/PHIP?.Coating's phases and microstructure were analyzed by XRD and SEM-EDS,respectively.Coating's surface hardness and the bonding strength between coating and matrix were measured by micro-hardness tester and impact test,respectively.The corrosion resistance and anti-thermal fatigue property of coatings were tested by 2h hot aluminum liquid corrosion test and thermal fatigue test machine,respecitively.The main conclusions are as follows:1.The coatings consist of fine size and uniform distribution TiC particles with Ni phase closely and uniformly around.And the Ni/TiC coating is bonding well with the H13 steel matrix because of the functionally gradient layer.2.With the increase of preheating temperature,the coating densification,surface hardness,TiC particles size and bonding strength between coating and matrix increase and the Ni content reduces.3.After 2h aluminum corrosion test,failure depth of Ni/TiC coating was quite big and AlNi₃ particles adhered to coating surface.The AlNi₃ particles became smaller in the grain size and decreased in number with the increase of the preheating temperature.4.The molten aluminum corrosion mechanism is mainly the corrosion of metal Ni and the oxidation of TiC on coating surface and the corrosion of metal Ni inside the coating.5.After 600 thermal fatigue circles,only the 25?coating bread off.For 100?coating,transition layer segmentation cracks were produced by the propagation of crarks initiated in the interlayer.For 200?and 300?coatings,thermal fatigue cracks of interlayer didn't propagate into matrix and along the coating-matrix interface.And thermal fatigue cracks became smaller with the increase of preheating temperature.6.Hot fatigue cracks initiated at the defect tips of coating surface and interlayer and propagated in TiC particles with typical character of transgranular fracture which belongs to brittle rupture.