Conference Report: NIST-INDUSTRY WORKSHOP ON THERMAL SPRAY COATINGS RESEARCH Gaithersburg, MD July 20, 1992

In 1992, a comprehensive survey of current Federal materials research programs and plans for new initiatives, known as the Advanced Materials and Processing Program (AMPP), was developed under the auspices of the Office of Science and Technology Policy. The goal of the AMPP is to improve the manufacture and performance of materials to enhance the nation's quality of life, security, industrial productivity, and economic growth [1]. One element of the program addresses what have become known as "Functionally Gradient Materials" (FGM). This class of materials is distinguished by properties which vary with material thickness. These gradients in properties such as hardness, thermal conductivity and chemical stability contribute to the improved performance of components. For example, the wear resistance of a soft but tough material can be greatly improved by the application of a harder but compliant surface deposit overlayed with a very hard but brittle material. The concept of gradations of material properties to optimize performance is not new but increased awareness of the opportunities for improved control of properties and the ability to tailor microstructures continuously through a thickness has fostered a view of these materials as a distinctive class whose potential has not been fulfilled. Typically these materials' compositions vary from metallic to ceramic over a thickness of up to several millimeters. The unique approach now taken to graded materials in FGM research is to target specific properties at the extremes of the material's thickness, thermal conductivity, and thermal expansion, for example, and to tailor microstructure, porosity or other features to meet those properties. Extensive research to achieve this capability through understanding of processingmicrostructure-property relationships has been initiated through material synthesis techniques as varied as thermal spray, chemical vapor deposition, and self propagating high temperature synthesis [2]. Thermal spraying of coatings, due to high material deposition rates and relatively low capital cost, has become a primary industrial method of synthesizing materials with varying composition and microstructure. The North American thermal spray market was over $600 million in 1990 and is projected to reach $2 billion per year by the year 2000, a growth rate of 7-8% per year. The largest portions of this market are in powder consumables and coating services. The growth projected is largely based on the increased use of ceramic coatings for thermal barriers and clearance control on aircraft gas turbines, some of which have close to 5500 parts which are thermal spray coated [3]. Similarly, the market for ceramic powders used in