Variation of WC grain shape with carbon content in the WC–Co alloys during liquid-phase sintering

The structure and magnetic properties of model high-cobalt WC–50%Co alloys with different carbon content and 1,6–5,6 wt.% TaC additives are studied. Model alloys are obtained by liquid-phase sintering of powder mixtures at 1420 °C, and their composition is described by the formula: 50%Co + 50%WC + xTaC + yC, where x = 0; 1,6; 2,6; 3,6; 4,6; 5,6 wt.%, y = 0; 0,2; 0,5 wt.%. It is shown that (Ta,W)C phase precipitates are present in all the investigated alloys, whereby at up to 3,6 wt.% TaC concentration the (Ta,W)C grains have a needle shape, and at ³3,6 wt.% TaC concentration the shape of the (Ta,W)C grains becomes spherical. (Ta,W)C phase precipitates are located both in the Co-binder and along the WC grain boundaries. The (Ta,W)C phase lattice parameter in low-carbon alloys lies in the range from 0,4438 nm for the 1,6 % TaC alloy up to 0,4451 nm for the 4,6 % TaC alloy. According to EDX analysis, the concentration of dissolved tungsten in the cobalt phase is independent of the TaC content and strongly depends on the total carbon content, and for alloys with high, elevated and low carbon content it is 7, 12 and 17 wt.%, respectively. TaC addition in alloys with a low and elevated carbon content leads to an increase in coercive force by 875 A/m and a decrease in magnetic saturation by 5–10 Gs·m3/g. The experimental results allowed putting forward a hypothesis about the possibility of forming dispersed tantalumcontaining precipitates in the binder phase.

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A direct observation of the grain shape accommodation during liquid phase sintering of Mo“Ni alloy

Scripta Metallurgica et Materialia ◽

10.1016/0956-716x(90)90139-8 ◽

1990 ◽

Vol 24 (5) ◽

pp. 927-930 ◽

Cited By ~ 10

Author(s):

Dong-Duk Lee ◽

Suk-Joong L. Kang ◽

Duk N. Yoon

Keyword(s):

Liquid Phase ◽

Direct Observation ◽

Grain Shape ◽

Liquid Phase Sintering ◽

Ni Alloy

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Observation of grain shape accomodation during liquid phase sintering

Metal Powder Report ◽

10.1016/0026-0657(90)90968-m ◽

1990 ◽

Vol 45 (10) ◽

pp. 719

Keyword(s):

Liquid Phase ◽

Grain Shape ◽

Liquid Phase Sintering

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Effect of furnace atmosphere and silica content on the consolidation behaviour of magnesia partially stabilised zirconia

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100178410 ◽

1990 ◽

Vol 48 (4) ◽

pp. 1056-1057

Author(s):

J. Drennan ◽

R.H.J. Hannink ◽

D.R. Clarke ◽

T.M. Shaw

Keyword(s):

Liquid Phase ◽

Silica Content ◽

Liquid Phase Sintering ◽

Furnace Atmosphere ◽

Boundary Phase ◽

Analytical Electron ◽

Analytical Electron Microscope ◽

Series Of Experiments ◽

Compositional Gradients ◽

Mobile Liquid

Magnesia partially stabilised zirconia (Mg-PSZ) ceramics are renowned for their excellent nechanical properties. These are effected by processing conditions and purity of starting materials. It has been previously shown that small additions of strontia (SrO) have the effect of removing the major contaminant, silica (SiO2).The mechanism by which this occurs is not fully understood but the strontia appears to form a very mobile liquid phase at the grain boundaries. As the sintering reaches the final stages the liquid phase is expelled to the surface of the ceramic. A series of experiments, to examine the behaviour of the liquid grain boundary phase, were designed to produce compositional gradients across the ceramic bodies. To achieve this, changes in both silica content and furnace atmosphere were implemented. Analytical electron microscope techniques were used to monitor the form and composition of the phases developed. This paper describes the results of our investigation and the presentation will discuss the work with reference to liquid phase sintering of ceramics in general.

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