Papers by Keyword: Powder Material

Abstract: The paper presents the results of the computer modelling of the stressed state and relative density when burnishing a porous hollow cylinder, made from copper sintered powder material. The mathematical model, based on the theory of porous bodies’ plasticity, is used for the analysis. The paper researches the impact of the initial porosity of the material on the effective stresses distribution, relative density and force change when free burnishing of hollow cylinders. It is ascertained that with the decrease of the initial porosity of the sintered material there is the increase of the burnishing force, stresses rate and relative density on the inner sur-face of a hollow cylinder. For porous materials at a certain stage of burnishing, the deformation zone is transformed into the compaction zone with a high relative density which de-creases while moving away from the inner surface of hollow cylinders. The maximum value of the relative density is implemented directly on the inner surface of hollow cylinders; along with this the density value is evenly distributed on the inner wall.

Abstract: Mass transfer in the laser-interaction zone at selective laser melting influences the quality of the obtained material. Powder particles displacement during the formation of the single bead is experimentally studied. The so-called denudated zone was visualized by metallography. It was determined that increasing the powder particle size leads to widening the denudated zone. This can signify that the adhesion forces between powder particles prevail over the friction forces.

Abstract: The interaction of components and structure formation were studied in liquid phase sintering of Co-Sn and Co-Sn-Cu powder materials. The powders of commercially pure metals were mixed with an organic binder and applied on the steel substrate. Sintering was performed under vacuum at temperatures of 820 and 1100 °C. The structure of sintered alloys was investigated by X-ray diffractometry and electron probe microanalysis, and microhardness (HV_0.01) of the structural components was measured. It has been found that the nature of interaction of the liquid tin with the solid phase at the initial stage of sintering affects the formation of structure and porosity of Co-Sn and Co-Sn-Cu alloys considerably. In Co-Sn alloys, diffusion of tin into cobalt particles leads to the formation of intermetallic compounds, which hinders spreading of the liquid phase. This results in a porous defect structure formed in Co-Sn alloys. In Co-Sn-Cu alloys, at the initial stage of sintering the liquid phase enriched with copper is formed that wets the cobalt particles and contributes to their regrouping. As a result of this, materials with minor porosity are formed.

Abstract: This paper discusses the mathematical model of powder material particles heating in the gas flow when applying plasma gas and thermal coatings. It has been assumed that while moving in the plasma, the particle is heated by convective heat transfer and radiative heat transfer. To ensure accuracy and validity of calculation, two characteristic regions have been outlined: Core, where the temperature, density, and viscosity of plasma, as well as the other parameters are assumed as constant; and the region from the core to the coated surface (substrate), where these parameters are the functions of the plasma flow coordinates. One of the assumptions is that the shape of the particles is near-spherical, and the thermal flow’s action to the particles’ surface is uniform. Special attention has been paid to correct selection of criteria , which allowed to simplify the solution and reduce it to the ordinary first-order differential equation derived from the particle heat balance equation.

Abstract: This article provides the reader with results of the study of mesostructure ordered plasma ceramic coatings derived from narrow-fraction powders under optimum modes for this fraction. It is noted that it is succeeded to implement mesostructure ordering of coatings eliminating the formation of continuous columnar structures by means of spraying mode control. It is proven that it is possible to get formation of nanocolumnar structures in a near surface layer, and these structures provide bonds damping between clusters under alternating force and thermal loads of coated parts. To evaluate the quality of formed ordered structure, a quantitative criterion—mesostructure ordering coefficient—is used. The Methods of quantitative evaluation of mesoordering of coating structure has been developed.

Abstract: The article presents a study of selective laser melting process (SLM) namely a study of stable track formation by the example of Co-Cr alloy. The characterization of the main process factors, which have an influence on the parts’ functionality, is developed. The experimental work for the research of two main factors as laser beam power and scanning speed showed the technological gaps for the formation of the stable tracks. The characterization of the non-stable single tracks’ defects is established. The new data about the main physical effects in the treatment zone is received by optical diagnostics of the process.

Abstract: Titanium and its alloys have been widely used for medical and aerospace applications because of their excellent attributes of light metal, high strength, high corrosion resistance and high biocompatibility. Especially, Ti-6Al-7Nb alloy has been developed as a more suitable biomaterial to replace Ti-6Al-4V alloy, because vanadium is toxic element to the biological body. However, it is not easy to fabricate the complex shaped and precise parts by the conventional methods due to their poor castability and machinability. In this study, laser forming technique has been applied to solve the above problems. The precise structure was obtained by optimizing the laser forming parameters. Using this technique, a honeycomb structure was fabricated　effective to grow the neighboring tissue and also encourage osseointegration. Finally, mouse osteoblasts were cultured on the formed structures, resulted in the effectiveness of the honeycomb structure for biocompatibility.

Abstract: A comparative study of two analytic solutions for the classical plasticity of incompressible materials and a plasticity model for powder materials is made to reveal an effect of plastic compressibility on qualitative behaviour of the velocity field in the vicinity of maximum friction surfaces.

Abstract: During the research the following problem was raised: to define the pulse laser radiation influence value on different powder materials, as well as to define experimentally the thickness and width relations of a sintered powder layer from technological laser radiation parameters.