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TZM Alloy Hot-dip Aluminum Coating Microstructure

TZM alloy has good high temperature performance and mechanical properties, often as heat-resistant and high-temperature structural materials widely used in nuclear reactors, aerospace, power generation and chemical industry, but it is easily oxidized in air at high temperature, thus greatly limiting its applications. Use hot-dip aluminized process to produce aluminum layer on TZM alloy surface, which can improve the high temperature oxidation resistance. After 800 ℃, 100h cyclic oxidation experiment found that TZM alloy surface coated on aluminum layer its high-temperature oxidation resistance is greatly improved. The coating consists of surface pure aluminum alloy layer and inner alloy layer and the mainly metallurgical of alloy layer is Al₄Mo and Al₅Mo phase.

TZM alloy after hot dip aluminum coating, its surface shows shiny metallic luster and surface is roughness, seamless plating. Observed alloy hot dip aluminum coating microstructure found, after hot dip aluminum coating the metallographic structure of alloy includes brown inlay, pure aluminum layer (I), alloy layer (II) and matrix (III). Besides, the coating is uniform and compact, divided into outer and inner layers, distinct phase interface. In addition, the study found that, at the same temperature of hot-dip, longer dipping time, the thickness of the alloy layer also increases.

Measured aluminum coated layer cross section microhardness found that the outer surface has lower hardness. When the hardness of load is 25g, the hardness range is HV30 ~ 130, which is mainly dependent on α-Al. With distance from the surface increasing, the hardness also increases. In 120um, the hardness value reaches HV760. In 120 ~ 150um, hardness changes at the range of HV760 ~ 758 and the hardness load is 500g, mainly because alloy layer Al₄Mo and Al₅Mo is cemented carbide phase having greater hardness. Then, as the distance further increase, the hardness begins to decline sharply, remained steady at HV260, where the hardness load is 100g and TZM alloy matrix hardness is HV260.

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