WC-Co Carbide Research Articles

Friction behaviour of heat isolating coatings in machining: mechanical, thermal and energy-based considerations

This paper deals with possible modifications of the frictional behaviour exhibited during the cutting process resulting from the influence of the most-commonly used heat isolating coatings deposited on a WC-Co carbide substrate. For this study, three- and four-layered coatings with intermediate Al 2O 3 ceramic layer and a monolayer TiAlN coating, which offer superior thermal protection of the carbide substrate, were examined. Orthogonal cutting tests were carried out by end-turning medium carbon steel and austenitic stainless steel workpieces. The experimental study was aimed at determining the fundamental frictional characteristics: dimensions of the tool-chip contact area, the friction force, the mean friction coefficient, the specific frictional energy and the corresponding thermal effects: the contact temperature and the frictional heat flux. Subsequently, results obtained for the mechanical, energy-based and thermal approaches to the frictional behaviour occurring in the carbide/ceramic coating-steel tribo-pairs were verified experimentally and the results obtained are discussed in detail.

Microstructure Evolution in the Cemented Carbides WC-Co II. Cumulated Effects of Cr Additions and of the C/W Ratio on the Crystal Features of the WC Grains

The influence of an addition of Cr, introduced to replace 5 at% Co on the microstructure evolution of WC-13 at% Co with different C/W ratio is examined at 1450 °C. Three alloys consisting of WC and Co binder and containing a graphite or η excess are studied by SEM and TEM. The effects of Cr are similar to those induced by a W excess in the undoped alloys: decrease of the mean grain growth and change of the interface features of the WC grains. The interface modification — less faceted, with steps — indicates a decrease of interface energy anisotropy and suggests a coarsening mechanism limited by the growth of the steps. The specific role of Cr on the hindrance of large grain formation depends on the C/W ratio.

Effect of WC Particle Size on the Abrasive Wear of Thermally Sprayed WC-Co Coatings

Four types of WC-Co powders with different WC particle sizes are sprayed to produce WC-Co coatings with a Jet-Kote gun using a gas mixture of C2H2–30% C3H6 and pure propylene as fuel gases. The carbide size in sprayed high velocity oxy-fuel (HVOF) WC-Co coatings is measured from the microstructure. The abrasive wear of the coatings is characterized using a Suga abrasive wear tester. The abrasive wear mechanism of thermally sprayed WC-Co is discussed. The relationship between the relative wear of WC-Co coatings and carbide sizes is established according to the strength theory on hard alloy. The correlation with experimental data proves that the relative abrasive wear of WC-Co coating is proportional to square root of relative carbide size.

On Strength Design of the High Pressure Compound Vessels Classic Fitted in and Wound Construction.

The two levels strength design methodology is presented. First the optimal main vessel dimensions and overlaps, resp. ribbon prestressing are assessed utilising the simplified geometrical and material model, namely the equivalent cylindrical compound vessel and linear elastic material. On the second computational level the more precise stress and strain analysis is performed with the help of problem oriented finite element method (FEM) code PROKOP, taking into account the nonstationary temperature field, elastic-plastic material behaviour, crack presence etc. and also the whole loading history including the assembly and disassembly process. The strength condition for sintered carbide WC-Co in the form of modified brittle fracture criterion was utilised and mixed computational-experimental approach for the low cycle lifetime determination has been proposed.

On the use of the MMI-phenomenon for the formation of nanostructures in WC-CO cemented carbides

The regularities have been studied of the development of nanostructures in WC-Co cemented carbides in precipitating new dispersion phases from Co melt. Cobalt melts alloyed with Ti, Ta, Nb, Cr, Fe, Ni and Re, have been introduced into sintered specimens using the MMI-phenomenon. Three types of nanostructures which form in WC-Co carbides have been observed. It is shown that the formation of a specific nanostructure is dictated by the formation energy of a carbide of a metal being introduced. Using this fact one can control the formation of nanostructures in WC-Co cemented carbides and purposefully change physico-mechanical properties of the latter.

FEM modelling of the elastic-plastic stress and strain of an axisymmetrical compound vessel with a component made of sintered carbide

A problem oriented calculation method has been developed, using a displacement version of FEM, which models all significant phenomena connected with the assembly and exploitation of an axisymmetrical compound vessel. First the mathematical formulation of the constitutive relations is presented, based on the associated theory of plastic flow. The von Mises' plasticity criterion was applied together with the mixed hardening rule. An appropriate modification was suggested for sintered carbide WC-Co, which exhibits a different behaviour in tension and compression. An inhomogeneous temperature field and its influence on mechanical properties is taken into account. The deformation loading at contact surfaces is simulated with the help of linear combinations between the displacement increments in nodes. A special calculation procedure has been proposed to simulate the assembly process. To demonstrate the possibilities of the calculation method, one practical example is presented.

ＷＣ‐Ｃｏ系超硬合金の拡散被覆 低温浸炭に関する二，三の考察

The author has been unable to find any reports on the carburizing of cemented carbide WC-Co systems at temperatures of the order of 500-600°C.In this study, at low temperature a cemented carbide WC-Co system was carburized to examine the applicability of the paste process to cemented carbide used for wood cutting tools.It was found that:(1) WC-Co cemented carbide system increased in mass after carburization and the rate of mass gain depended on Co content and acceleration factors.(2) A layer containing Co2 C was formed in a very short time on the WC-Co alloy surface.(3) Hardness increased with both longer time and higher temperature carburization, but transverse rupture strength decreased.(4) Low Co alloys could be hardend by carburization in the same way as iron and steel, but toughness was decreased. The use of higher Co content alloys and lower carburizing temperatures will be effective in obtaining alloys that were of tough and also applicable to cemented carbide tools.

ＷＣ‐Ｃｏ系超硬合金の拡散被覆 ボロナイジングとシリコナイジングについて

There are solid, liquid and gas processes in the diffusion coating technics and the first one is divided into a number of practical technics using paste, powder, etc. Moreover, this technics has lots of variations such as single, composite and progressive processes.By means of combination of the above mentioned processes and a high frequency heating method, it is expected that hardness, resistivity to abrasion, toughness and durability of cemented carbides can be improved considerably.Results obtained in this study are summarized as follows.(1) Cemented carbide WC-Co system increased its weight after the treatments of boronizing without any protection atmosphere and its increasing rate depended on the Co contents in the alloy. On the contrary, siliconizing treatment in the same atmosphere caused to decrease its weight because of peeling.(2) Intermetallic compounds formed by these reactions were identified by the X-ray diffraction pattern. They were Co3B in boronizing and Co2Si in siliconizing.(3) Changes of hardness and transverse rupture strength of this alloy after these treatments depended on the treated conditions; in boronizing disproportionally, but in siliconizing proportionally.(4) In order to carry out siliconizing effectively, a high temperature treatment more than 1000°C is recommended.

Application of dihedral angle measurements to the microstructure of cemented carbides WC-Co

Dihedral angle measurements on sintered WC-Co reveal preferred contact angles between particles and preferred particle orientation over short distances.