Tungsten Carbide-cobalt Alloys Research Articles

Electrochemical behavior of tungsten carbide-cobalt alloy using molten hydroxide as electrolyte under low temperature

Tungsten carbide-cobalt alloys (WC–Cos), which are used for cutting tools, are mainly composed of tungsten carbide and cobalt with minor elements including chromium, tantalum, nickel. Recycling WC–Cos requires a large amount of energy and chemicals for leaching tungsten. We previously showed that tungsten in WC–COs can be leached by potentiostatic electrolysis at − 0.7 V in molten sodium hydroxide (NaOH) at 723 K; tungsten constituted 99.7 mass% of the leached component in the molten salt. In this study, we investigated tungsten leaching at a lower temperature by using a eutectic mixture of 51.5 mol% NaOH and 49.5 mol% potassium hydroxide (KOH) as the electrolyte. Tungsten was leached from the alloy at temperatures above 623 K, which was 100 K lower than the previous study. Cobalt dissolved in the molten salt, although it formed a passive layer. Chromium underwent oxidization and dissolved as a hexavalent ion below 623 K. Tantalum dissolved even without electrolysis. Tungsten was leached at 623 K in this system. Highly purifying tungsten could be obtained by dissolving the cooled molten salt in water and bringing it in contact with air to precipitate other metal ions. Therefore, the electrochemical process is expected to be used for separating tungsten from WC–Cos.

Inhibition of grain growth in sintered nano-phase tungsten carbide-cobalt alloys : R.J.Sadangi et al. (Rutgers University, NJ, USA.) Int. J. Powder Metall., vol 25, no 1, 1999, 27–33

Inhibition of grain growth in sintered nano-phase tungsten carbide-cobalt alloys : R.J.Sadangi et al. (Rutgers University, NJ, USA.) Int. J. Powder Metall., vol 25, no 1, 1999, 27–33

Experimental study of the mechanics of fracture in WC-Co alloys

Tungsten-carbide cobalt alloys in the range of technically relevant compositions an microstructures were fractured under controlled conditions. Stable and unstable crack propagation are shown to be equivalent with respect to crack geometry and energy release rates. Based on microscopic observations and on measurements using SEM micrographs, the nature of the process zone, the maximum extension of plastic deformation, the types of crack paths, and the area fractions of these crack paths are determined. The results, which are in partial disagreement with earlier work, provide the basis for the qualitative understanding and the quantitative description of fracture processes in composites combining a ductile phase embedded in a brittle matrix.

Effect of residual porosity on the fatigue life of tungsten carbide-cobalt alloys subjected to cyclic cantilever bending

Effect of residual porosity on the fatigue life of tungsten carbide-cobalt alloys subjected to cyclic cantilever bending

Factors Influencing the Rupture Stress of Hardmetals

AbstractAn attempt has been made to establish the role of several parameters in relation to the rupture stress in bending and compression for 24 different compositions of tungsten carbide–cobalt alloys. Particular attention was paid to the microstructural parameters which had the greatest effect on the rupture stress. It was possible to confirm the uniformity of these materials using the statistical analysis of Weibull. The Weibull coefficient was shown to be related to certain microstructural parameters such as the contiguity. The study of the initiation of microcracks enables one to introduce the microstructural parameter L2Co/D wc. This ratio correlates very well with the values for stress to rupture in bending and in compression.

The formation of tungsten carbide in cobalt-base wear-resistant coating alloys

Tungsten carbide-cobalt alloys cannot be produced by melting because of a peritectic reaction in the W-C system; they are produced by sintering. Tungsten carbide-cobalt powders (mixed, agglomerated, sintered) can be plasma sprayed or deposited by other techniques but they cannot be fused afterwards without decomposition of the tungsten monocarbide that provides the best mechanical properties for many applications. Wear-resistant cobalt alloys were developed 60 years ago and are based on cobalt-chromium-tungsten-carbon. During studies of the CoCrWC system with various carbon concentrations and at various temperatures we identified MC, M 2C, M 7C 3, M 23C 6, M 6C, M 12C and M 28C carbides. The solidifying M 6C carbide is unstable over a certain concentration range of chromium and decomposes to form tungsten carbide (WC). On heat treatment the tungsten-containing M 6C forms WC in a cobalt-chromium matrix if the chromium content is less than 5 wt.%. It is therefore possible to produce a sprayed and fused or welded layer of WC-cobalt alloy. The rate of WC formation depends on temperature and time. Time-temperature-decomposition diagrams have been established for four alloys. The structures of the heat-treated alloys are similar to those of sintered tungsten carbide-cobalt alloys.

WEAR OF HARD-METALS IN ROCK DRILLING: A SURVEY OF THE LITERATURE

AbstractThe literature concerning the wear of tungsten carbide-cobalt alloys used as tool bits in rock drilling is surveyed. The possible mechanisms of rock breakage and of tool wear are briefly discussed. Wear takes place as a result of shock impact or impact-fatigue spalling, by abrasion-mainly from the quartz grains in the rock, and also by thermal fatigue. The mechanism that dominates in any given conditions depends on the method of drilling and on the strength and abrasiveness of the rock. For rotary-percussive drilling, impact-fatigue wear and abrasion operate simultaneously,though essentially independently.Published data on the relations between the wear of WC-Co alloys in rock drilling and their structure and properties are critically discussed. It appears that the resistance to impact wear is a direct function of the bulk compressive or transverse rupture strength and is related to the WC grain size and the Co mean free path. It is directly proportional to the blow energy in percussion. The resul...

A STUDY OF THE FACTORS CONTROLLING GRAIN SIZE IN SINTERED HARD-METAL

AbstractPrevious experimental work concerning the grain growth observed during the sintering of tungsten carbide–cobalt alloys is reviewed. Particle-sizing methods suitable for the examination of hard-metal powders are described, and techniques for the evaluation of the carbide grain size in the sintered compacts are discussed.By using a Model A Coulter Counter to examine the size distribution of the carbide grains (obtained from the milled hard-metal powders by dissolution of the cobalt with hydrochloric acid), and by counting techniques on electron photomicrographs of carbon replicas of the sintered compacts, it has been established that the increase in grain size during sintering is quantitatively related to the carbon content of the material after pre-heating. The results presented indicate that the cobalt content exerts little influence on the average grain size of the sintered structures A cobalt content >10% by weight is shown to exert a strong damping effect on the rate of comminution during milli...

A REVIEW OF PARAMETERS INFLUENCING SOME MECHANICAL PROPERTIES OF TUNGSTEN CARBIDE–COBALT ALLOYS

The paper reviews experimental results relating to the influence of composition, structure, and testing conditions on the hardness, compressive strength, and transverse rupture strength of sintered tungsten carbide–cobalt alloys.

Elevated temperature compressive creep behavior of tungsten carbide-cobalt alloys

The compressive creep deformation of two-phase tungsten carbide-cobalt alloys with 12 and 15% Co has been investigated at temperatures of 800, 900, and 1000°C for stresses of 10,000 to 110,000 psi. At each temperature studied, the WC-Co alloys showed a decreasing steady-state creep rate with increasing WC particle size for low creep-stress levels. At high stress levels, the steady-state creep rate was observed to increase with increased WC particle size. These observations, with additional considerations of the creep behavior, indicated that two mechanisms were rate determining during deformation of WC-Co alloys. To ascertain the rate-determining mechanisms during deformation, existing creep models were extended to include the high volume loading of dispersed WC particles present in these alloys. At high stresses, the mechanism postulated to describe steady-state creep deformation was the looping of dislocations in the Co matrix between WC particles and the climb of pinched-off loops. The diffusion of Co in the matrix around WC particles has been suggested as the rate-controlling steady-state creep mechanism at low stresses.

WC-Co合金の疲労について

The influence of cobalt content on the fatigue strength and fatigue phenomena in tungsten carbide-cobalt alloys were investigated. The test was done at 8000 rpm by using a rotating beam fatigue machine.The results obtained are as follows:(1) The S-N curves in WC-Co alloys do not show flat portions which are observed in the case of iron and steel materials. Taking N=108 rpm for the fatigue limit, the fatigue strength increases with cobalt contents. There is a linear relation between fatigue strength and tensile strength.(2) Enlarged pictures of the fatigue fracture surface indicate that the crack runs emissively, with the stress concentration source as the central figure. Electromicrographs of the crack source neighborhood exihibit a kind of fusional structure. This fusional part may be due to the excessive stress concentration.(3) According to the results of X-ray diffraction, the binder phase transforms from γ Co (fcc) to ε Co (hcp) by fatigue and it’s ε content increases with fatigue degree.(4) The coercive force increases with increasing fatigue and stress.

Role of the Binder Phase in Cemened Tungsten Carbide-Cobalt Alloys

Role of the Binder Phase in Cemened Tungsten Carbide-Cobalt Alloys