David L. Houck

Effect of Carbide Grain Size on the Sliding and Abrasive Wear Behavior of Thermally Sprayed WC-Co Coatings

The carbide size and cobalt content of thermally sprayed tungsten carbide/cobalt coatings (WC-Co) can influence their microstructure, fracture strength, friction response and abrasion resistance. In this paper, these properties have been determined for one commercially available and three experimental WC-17 wt.% Co thermally sprayed coatings. The experimental coatings were processed from starting powders containing median carbide size distributions of 1.2, 3.8 and 7.9μm, respectively. All the coatings were produced using a high velocity oxy-fuel (HVOF) spray process. The present results indicate that coatings with a higher percentage of finer carbide size distribution in the starting powder display a higher degree of decomposition of the WC phase to W2C phase and, consequently, display lower fracture toughness and abrasion resistance values. Unidirectional, unlubricated sliding wear tests did not reveal major differences in the sliding wear response of the coatings as a function of carbide size. The micro...

Current Problems in Plasma Spray Processing

This article summarizes eight contributions from a thermal spray conference that was held in late 1991 at Brookhaven National Laboratory, Upton, Long Island, New York. Plasma spray processing is discussed in terms of plasma-particle interactions, deposit formation dynamics, thermal properties of thermal barrier coatings, mechanical properties of coatings, feedstock materials, porosity, manufacture of intermetallic coatings, and synchrotron X-ray microtomographic methods for thermal spray materials. Each section is intended to present a concise statement of a specific practical and/or scientific problem. It then describes current work that is being performed to investigate this area, and finally suggests areas of research that may be fertile for future activity.

Consolidation of tungsten-coated copper composite powder

Powder metallurgy (P/M) methods have expanded in recent years to include net-shape fabrication of W-Cu components. Sintering of W-Cu compacts made from previous powders has led to low density and copper bleedout. This paper presents test results on the consolidation of a new powder containing particles composed of a tungsten-coated copper core. This powder effectively eliminates copper bleedout at sintering thereby making possible the net-shape manufacturing of parts. Sintered articles are characterized by microstructural homogeneity and properties comparable to those of infiltrated W-Cu composites.

Synthesis and hydrogen reduction of tungsten–copper composite oxides

Cupric tungstate (CuWO 4 ) can be synthesized at high rates of conversion from a variety of solid reactants. However, the fixed copper content in the metal phase of CuWO 4 limits its use as an oxide precursor for making W-Cu composite powders. This paper presents test results on synthesis of CuWO 4 -based composite oxides with a variable content of copper in the metal phase (5-25.7%). Hydrogen reduction converts the oxides to W-Cu composite powders with a unique phase distribution: each individual particle consists of a tungsten phase and a copper phase in which the tungsten phase substantially encapsulates the copper phase. These powders, when pressed and sintered without activators, yield high-density parts with a very fine microstructure and high electrical and thermal conductivity.