Search

A new titanium aluminide coating method on titanium surface has been proposed, which is characterized by arc surface melting of an aluminum plated titanium surface. The arc surface melting was performed using a computer aided 3-dimensional micro welder (3DMW) designed by the present authors. The arc heat melted the aluminum plated titanium surface and produced a titanium aluminide layer of a ~300 μm thickness on the surface of titanium substrate. The titanium aluminide coated sample exhibited 500–700 in Vickers hardness number and excellent wear resistance.

A new welding method was proposed based on the self-propagating high-temperature synthesis (SHS) reaction between droplets and powder of elemental metals, and its feasibility was investigated in a simple experiment. In the experiment, an aluminum droplet was dropped onto nickel powder heaped up in a groove at the interface between two NiAl substrates. The aluminum and nickel exothermically reacted and produced intermetallic compounds in Al-Ni system, and the NiAl substrates near the interface were melted by the heat from the reaction. The microstructure of the reaction products varied depending on the initial temperatures of the aluminum droplet and nickel powder and also the groove spacing. Increase in initial temperatures of the aluminum droplet and nickel powder and the groove spacing promoted both the exothermic reaction to synthesize NiAl in the groove and the melting of the joint surface of the substrates.

Two new different methods for coating aluminide intermetallic compounds on metals have been proposed : one is based on exothermic reaction between droplets of aluminum liquid and metal powder, while the other is based on arc surface alloying with aluminide forming metals. The feasibility of the former method was experimentally investigated using NiAl and SUS 316L stainless steel as demonstration coating material and base material, respectively. As soon as an aluminum droplet was dropped onto the nickel powder that had been placed on steel surface, the droplet and powder exothermically reacted and produced a superheated NiAl liquid bead on the steel surface, and the heat of the liquid bead melted the contact surface of the steel. The superheated NiAl liquid bead solidified on the steel surface, leading to NiAl coating on the steel. On the other hand, the feasibility of the latter method was experimentally confirmed by NbAl3 coating on niobium. When tungsten arc was used to melt an aluminum sheet placed on a niobium plate, the niobium surface was also melted and a melt pool of Al-Nb alloy was formed on the niobium plate. The melt pool solidified into layers of niobium aluminides on the surface of the niobium plate, forming a thick NbAl3 layer on the top surface of the niobium aluminides layers.