Zirconium boride and tantalum carbide coatings sprayed by electrothermal explosion of powders
- PDF / 4,086,460 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 69 Downloads / 135 Views
International
Zirconium Boride and Tantalum Carbide Coatings Sprayed by Electrothermal Explosion of Powders 14. Tamura, M. Konoue, and A.B. Sawaoka
(Submitted 26 October 1996; in revisedform 18 February 1997) Refractory zirconium diboride and tantalum monocarbide ceramic powders were sprayed using an electrothermal explosion caused by a high-voltage electric breakdown and large-current discharge heating. This spray technique was improved using a purpose-designed powder container, which made it possible to melt the powder completely and accelerate it to impinge on substrates. The electrical energy applied to the powder was estimated to be about twice the energy theoretically needed to melt just the powder. Although the ceramics used in this work are hard-sintered materials by nature, they could be sprayed and deposited to form coatings on metal substrates without additives and sintering agents. The coatings formed exhibited no chemical decomposition in the boride, and only small amounts of decarburization in the carbide due to its nonstoichiometry. The tantalum carbide coating mixed with iron and aluminum substrates in the range of 10 ~tm to several tens of micrometers.
Keywords coatingmicrostructure,electrothermalexplosion, tantalumcarbide,zirconiumboride
I
1. Introduction Spray coatings of refractory metals and ceramics have been used in the fabrication of energy equipment, including gas-turbine engines, nuclear reactors, magnetohydrodynamic power generators, and steel-production equipment--all of which are operated under high-temperature conditions to enhance their performance. Increasing the operating temperature to accommodate higher performance requirements in the future will require coatings with improved properties. Some advanced ceramics exhibit excellent intrinsic properties without sintering agents. Although some refractory carbides, borides, and nitrides with high melting points and hardness can be used as fine ceramic coatings with heat and wear resistance, these materials usually are sprayed as cermets to suppress their oxidation and/or decomposition and to enhance interparticle bonding and adhesion to substrates. Under higher-temperature conditions, however, cermets lose heat resistance due to melting of their metallic component. This calls for development of a new method of spraying fine nonoxide ceramics with no additives, as well as examination of their properties as a tough coating under severe physical and chemical circumstances. This paper characterizes a new technique for the spraying of zirconium boride and tantalum carbide coatings without additives. Although the principles of this technique have been de-
H. Tamura, M. Konoue, and A.B. Sawaoka, Materials and Structures
Laboratory, Tokyo Institute of Technology, Nagatsuta 4259, Midoriku, Yokohama226, Japan.
Journal of Thermal Spray Technology
scribed previously (Ref 1), the present method results in improved spraying of refractory ceramic powders.
2. Description of Spray Method The technique uses powder particles of electrically cond
Data Loading...
