Sintered FeCuRe Alloys Produced from Commercially Available Powders

This paper discusses the mechanical properties of materials fabricated from commercially available powders designed for use as a metal matrix of diamond-impregnated composites. The powders with the catalogue numbers CSA and CSA800 produced in China were tested under laboratory conditions. The specimens were fabricated in a graphite mould using hot pressing. The materials were analysed for density, porosity, hardness and static tensile strength. A scanning electron microscope (SEM) was employed to observe the microstructure and fracture surfaces of the specimens. The experimental data was used to determine how the chemical composition of the powders and the process parameters affected the microstructure and properties of the materials. The properties of the sintered materials produced from the Chinese powders were compared with the properties reported for specimens fabricated from cobalt powder (Co SMS). Even though the hot pressed CSA and CSA800 powders had inferior mechanical properties to their cobalt analogue, they seem well-suited for general-purpose diamond-impregnated tools with less demanding applications.

Properties of Sinters Produced from Commercially Available Powder Mixtures

This paper discusses the mechanical properties of a material fabricated from commercially available metal powder mixtures designed for use as a metal matrix of diamond impregnated composites. The mixtures with the catalogue numbers CSA and CSA800 provided by a Chinese producer are suitable for experimental laboratory testing. The specimens were fabricated in a graphite mould using hot pressing. The material was tested for density, porosity, hardness, and tensile strength under static loading. A scanning electron microscope (SEM) was used to analyze the microstructure and cleavage fracture of broken specimens. It was essential to determine how the chemical composition and the fabrication process affected the microstructure and properties of the material. The properties of the sinters were compared with those of hot pressed specimens fabricated from sub-micron size cobalt powder (Cobalt SMS). Although the as-consolidated material is inferior to cobalt, it displays a favourable combination of hardness, yield strength and ductility, and seems to have a great potential for moderate and general purpose applications.

Detonation-Sprayed Wc-12%Co and Wc-17%Co Diamond-Impregnated Segments/ Natryskiwanie Detonacyjne Powłok Wc-12%Co I Wc-17%Co Na Spieki Metaliczno-Diamentowe

This paper presents results of investigations of WC-12%Co and WC-17%Co coatings detonation sprayed on a sintered cobalt substrate. The main objective of the present work was to establish a new production route of sandwich type diamond-impregnated segments for circular sawing of stone and other construction materials. Unalloyed cobalt was chosen as the substrate material. Prior to coating the specimens were made by means of hot pressing of Extrafine cobalt powder in a graphite mould. The segments were then coated with WC-Co. The effects of the coating process on the thickness, microhardness, microstructure and wear resistance of the deposits were investigated. The properties of the coatings were established by performing the following tests: a microstructure analysis, a point analysis of chemical composition and a linear analysis, a phase composition, a microhardness tests and abrasion resistance.

Effect of Mould Heating Temperature on Cooling Rate of the Melt upon Bronze Crystallization

The article presents the cooling curves of the tin-leaded bronze melt (consists of 10% of lead, 10% of tin, and 80% of copper) being poured in the moulds of various thermal conductivities: massive cast iron chill mould (with the 1:8 cast mass to mould mass ratio) and graphite mould. The curves were plotted for the moulds previously heated to the temperatures of 20; 200; 400; 600; 800 °С. Plotting of the curves was performed with the use of the device Thermograph designed at Tomsk Polytechnic University. The device records thermal electromotive force values of the chromel-alumel thermocouple and converts them into temperature values. The cooling curves are used to determine melt cooling rates within the temperature range involving the crystallization range. It is shown that under similar conditions the cooling rate when casting in cast iron mould is 30-40% higher than in the case of casting in graphite mould. The data given in the paper indicate that preheating of the mould enables us to considerably reduce the cast cooling rate and prolong the period of the melt being in liquid state. It is worth mentioning that cooling rate values of the preheated and non-heated casting moulds are most vividly observed at the initial moments after the melt pouring. When decreasing the casts’ cooling to 300-400 °С the cooling rates tend to be identical. In the article, the numerical data of cooling rates for various mould heating temperatures are presented.

Near Net Shape Forming Process of a Titanium Alloy Component Using Hot Isostatic Pressing with Graphite Mould

Ti6Al4V component has been formed by hot isostatic pressing (HIPping) using internal graphite mould with Ni isolation layer. The shape of the graphite had no deformation after HIPping. The Ni isolation layer with a thickness of approximately 5μm on graphite before HIPping was diffused into the dense Ti6Al4V component surface and formed a uniform, compact and crack free layer with a thickness of approximately 100μm after HIPping. The Ni diffusion layer is not damaged after removing the graphite mould by unpolluted sandblasting. The interface topography and the elements diffusion have been assessed and it is found that the non-machined surface of Ti6Al4V component was improved by using graphite mould than those used mild steel. The roughness of non-machined surface after removing the graphite mould by sandblasting is Ra=1.6μm, and the roughness of non-machined surface after removing the mild steel by acid pickling is Ra=10.8μm. It is concluded that graphite mould could be used for the HIPping process to produce complex-shaped components.

Investigation of Structures in As-Cast Alloys from the Mg-Zn-Ca System

Alloys of nominal composition Mg-3Zn-xCa (x = 0, 0.2, 0.5, 0.7, 1.0, 1.3) wt.% have been prepared by resistance melting and casting into graphite mould under argon atmosphere. All investigated alloys have revealed α(Mg) dendritic microstructures with intermetallic phases distributed in interdendritic spacing. The Mg4Zn7 has been identified as the main phase which coexists with α(Mg) in the Mg-Zn alloy. Calcium addition causes the formation of ternary Ca2Mg6Zn3 hexagonal phase, denoted also as Ca3MgxZn15-x . The increase of Mg/Zn ratio from 0.59 in Mg-3Zn-0.2Ca wt.% alloy to 2.72 in Mg-3Zn-1.3Ca wt.% alloy in this phase is connected with an increase in the lattice parameters. The microhardness of the Ca containing alloys increases up to 67 HV (for the alloy containing 1.3 wag.% Ca) compared to the 50 HV for Mg-3Zn wt.% alloy.

Solidification of A356 Alloy in a Linear Electromagnetic Stirrer

In the present work, a 2-pole linear electromagnetic stirrer (LEMS) is developed to study the effect of stirring during solidification of aluminium alloys. The stirrer design entails the placement of a stack of coils around the mold to generate a primary motion that recirculates along the longitudinal direction. The stirrer is first tested and validated by measuring the electromagnetic forces on solid aluminum cylinders of different diameters as a function of excitation current. The alloy to be stirred and solidified is placed in a cylindrical graphite mould located in the annulus of the LEMS. A suitable cooling arrangement is provided at the bottom of the mould to extract heat from the melt, in order to produce a rheocast billet inside the mould. Rheocasting experiments with A356 aluminium-silicon alloy are performed using a stirring current of 250A, in order to assess the effect of electromagnetic stirring on microstructure formation. The resulting microstructures and cooling curves with stirring are compared with those obtained without stirring.

THE SOLIDIFICATION MICROSTRUCTURE OF BIOMEDICAL TITANIUM ALLOYS UNDER THE CENTRIFUGAL FORCE

Two biomedical alloys, Ti -39 Nb -5.1 Ta -7.1 Zr ( TNTZ1 ) and Ti -35.3 Nb -5.1 Ta -7.1 Zr ( TNTZ2 ) were melted using LZ5 type centrifugal equipment for casting titanium. The solidification microstructures of TNTZ1 and TNTZ2 alloys cast in graphite crucible without centrifugal force are mostly big arborescent crystal with dispersed porosity in it. After pouring into a graphite mould under centrifugal force, the lower part of ingot showed mostly arborescent crystals with few equiaxed crystals, while the upper part of ingot is basically spherical equiaxed crystals. The solidification defects, such as dispersed pores were very difficult to find. Nb is supposed to refine the arborescent crystals. X-ray diffraction (XRD) analysis showed Ti -phase and Nb -phase existing in the above two alloys. The content of Ti was found relatively low in crystal interior and relatively high in crystal boundary. The content of Nb/Zr was uniform in whole microstructure.