Papers by Keyword: Liquid Phase

Abstract: Among the various alloying techniques used in powder metallurgy, the masteralloy concept has been known for a long time. However, its use for production of ferrous precision parts has been hampered by several obstacles such as poor output of the useful fine fractions, high tool wear and slow homogenization kinetics of the alloy elements in the matrix. On the other hand, the masteralloy concept is particularly interesting for introducing cost-effective alloy elements such as Cr, Mn and Si since the masteralloy approach at least alleviates the problems caused by the high oxygen affinity of these elements. In the present study it is shown that recent developments have given a boost to this classical concept, one of these developments being powder manufacturing by high pressure water atomization which dramatically increases the yield of fine masteralloy fractions. The other progress is availability of thermodynamic software that enables defining masteralloy compositions with low melting range and thus fast homogenization also at moderate sintering temperatures. Combined, these new developments open the door for implementation of the masteralloy route in large scale PM parts production.

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: Structure formation of diamond-containing composites with Sn-Cu-Co-W binders has been studied within the range of sintering temperatures of 780–820°C. The specimens were obtained by rolling the paste-like mixtures of metallic powders and diamonds on steel substrates, with sintering performed in vacuum. The structure of the sintered specimens was studied by optical metallography, X-ray diffractometry and electron probe microanalysis. Hardness of the materials was identified by Rockwell method (scale B). It has been found that the process of composites sintering is largely affected by oxide films available on the surface of the powders. In order to obtain composites having less than 10% porosity and up to 96–98 HRB hardness, they have to be sintered at the temperature of 820°C which eliminates the oxide films.

Abstract: The aim of this study was to evaluate the effect of Y₂O₃:Al₂O₃ additives and sintering temperature on thermal shock resistance of silicon carbide sintered via liquid phase. Silicon carbide samples containing 10 mol% Y₂O₃:Al₂O₃ (1:3 and 1:4) were prepared, compacted and sintered at 1750, 1850 and 1950 °C in a graphite resistive furnace. Thermal shock resistance was evaluated after each thermal cycle performed at 600, 750 and 900 °C followed by abrupt cooling in water. Samples with two Y₂O₃:Al₂O₃ proportions did not show major differences when sintered at the same temperature, though, rising the sintering temperature improves Y₂O₃:Al₂O₃ modified-SiC thermal shock resistance.

Abstract: Heat pipe is well known device which is used to heat transfer phase-change of working fluid. Pulsating heat pipe (PHP) is special type of heat pipe which heat transfer by pulsating movement of working fluid. Article deals about operating activity and thermal performance measurement of this special heat pipe. Operating activity visualization of PHP was performed with PHP made from glass. The two types of PHPs were made. The first PHP has internal diameter of tube 1 mm, second PHP has internal diameter of tube 1.5 mm and both PHPs have eleven meanders. The working fluids used in PHP were water and Fluorinert FC-72. These fluids were chose for their different thermo-physical properties and the visualization observe formation of liquid and vapour phase working fluid during filling process and working operation.Next, the article describes thermal performance measurement of PHP depending on working fluid amount and heat source temperature. Measurement was performed with PHP made from copper tube with inner diameter 1.5 mm curved to the twenty one meanders and filled with water. The results give us image about formation and distribution of working fluid in pulsating heat pipe and about influence of working fluid amount on the heat transfer ability of pulsating heat pipe.

Abstract: Quenching of steel 45 using high-frequency induction-heating (440000 Hz) with simultaneous shower water cooling was studied. The possibility of liquid-phase creation in the bulk (appr. 0.2 mm) in the material being treated in the absence of melting on the surface was clearly demonstrated by both numerical simulation of the temperature field in the material during hardening and experimental results

Abstract: Starting from the previously demonstrated twin-free 3C-SiC growth on 4H-SiC when using Ge pre-deposition treatment, this work focuses on the understanding of the growth mechanism that stands behind this result. Toward this end, short growth experiments were performed to allow the investigation of the nucleation stage. Based on the experimental observations, a mechanism is proposed which involves a Ge-induced transient homoepitaxial growth step followed by 3C nucleation when large terraces are formed by step faceting. Lateral expansion of the 3C islands leads to orientation selection and twin boundary elimination. Similar results can be obtained when applying a Si-based pre-deposition treatment so that the crucial transient homoepitaxial step is promoted in fact by the presence of a liquid phase itself, no by its chemical nature.

Abstract: This work presents the characteristic properties of powdered materials sintering under conditions of liquid-phase sintering. It has been established that to implement the liquid-phase sintering advantages it is necessary to do temperature research when the liquid-phase concentration does not exceed the critical one. The implementation of this condition provides the sintering temperature reduction by 150 – 200 °С.

Abstract: Viscosity, as one of important performance indexes of liquid-phase heat transfer fluids, its measurement methods and instruments have developed greatly in recent years. This paper introduces the traditional methods and theory of measuring liquid-phase heat transfer fluids’ viscosity as well as summarizes the development of measuring liquid-phase heat transfer fluids viscometer at home and abroad.

Abstract: This work is devoted to formation of the Widmanstatten ferrite in the zone of complete recrystallization of the base metal during welding of low-carbon steels and cladding of hard coatings on the surface of low-carbon steels. The methods to reduce the brittleness of the ferrite in the overheated zones are proposed.