Mullite/metal composite thermal barrier coating deposited by micro-plasma spraying

Mullite/metal thermal barrier coatings(MMCs) have been sprayed by micro-plasma spraying.The microstructure, bond strength, thermal barrier insulation and thermal shock resistance of the coatings have been investigated.The microstructure of MMC shows that mullite particles are surrounded by the metal lamellar structure.The average bond strength of the coatings is more than 30 MPa.The thermal barrier insulation of the coatings is improved with the increasing of surface temperature and the mullite fraction.At surface temperature of 1 175℃, the maximum thermal barrier insulation of coating is 125℃ with 70% mullite in the powder.The thermal shock resistance test, in which the specimens are heated up to 1 150℃ and then quenched in the water, shows that one of the main reasons for coating failure is substrate deformation.The thermal shock resistance of coatings is increased firstly, and decreased in succession quickly with the mullite fraction increasing, and the peak value of the thermal shock resistance is 72 times with 40% mullite fraction in the powder.