Papers by Keyword: Argon

Abstract: The positron annihilation lifetime spectroscopy (PALS) was applied to investigate the properties of capsules composed of n-alkanes (filling material) and polymer (shell) in the broad range of pressures up to 450 MPa. These microcapsules aggregate into the grains having about 200 μm in diameter. Their properties were investigated as a function of pressure (p) at several selected temperatures: when the filling material is in liquid, rotator and solid phase. Pressure experiments were performed without gas access to the sample and in an argon atmosphere. Two o-Ps components were found, the longer-lived correspond to the filler material, and the shorter-lived one – to the shell. These components change with p; even a small pressure (6 MPa) reduces considerably the o-Ps lifetimes (τ). At 303 K the o-Ps lifetime in the core changes non-monotonically, and at 60 MPa τ is higher than at 20 MPa. The increase of pressure induces the phase changes in the filling material, and also produces the deformation of microcapsule aggregates and crash of small capsules at the grain boundary region. Internal structure of the microcapsules was observed by SEM.

Abstract: The effect of argon content upon the growth rate and the properties of diamond thin films grown with different grains sizes are explored. An argon-free and argon-rich gas mixture of methane and hydrogen is used in a hot filament chemical vapor deposition reactor. Characterization of the films is accomplished by scanning electron microscopy, Raman spectroscopy and high-resolution x-ray diffraction. An extensive comparison of the growth rate values and films morphologies obtained in this study with those found in the literature suggests that there are distinct common trends for microcrystalline and nanocrystalline diamond growth, despite a large variation in the gas mixture composition. Included is a discussion of the possible reasons for these observations.

Abstract: Titanium alloys processed by the powder metallurgy route (PM) are sintered in vacuum, the higher the better. This philosophy is carried over to MIM titanium alloys. In the MIM process a large amount of out gassing of binders takes place, which affects the vacuum level and hence the interstitial element pick up in the titanium. In this paper the effect of gaseous material in vacuum is discussed and an alternate method of debinding and sintering in argon is proposed. Three processing conditions are applied to MIM tensile bars made from Ti-6-4 materials. First they are debound and sintered under high vacuum, second debound under argon and sintered in high vacuum and third debound and sintered in flowing argon. The physical properties and interstitial element contents are presented and the effects of the material structures due to different processing on the properties are discussed.

Abstract: The paper presents the results of the studies devoted to justification and development of methods and means of high-speed thin layer coating. It outlines the layer conditions formation, as well as the requirements for the individual components and surfacing installation assemblies. The following equipment items are designed and manufactured for the implementation of the developed coating processes: surfacing rack, feeding device rotating filler, surfacing head-die and others. The paper presents the completely temperature pattern detailed calculation program with differential-difference scheme-line obtained from a combination of explicit and implicit schemes. The mechanical properties, residual stress, fatigue strength, hardness and microstructure of the coating, etc. have been undertaken as well. The paper recommends the technology to restore worn surfaces of the cylindrical parts with little wear and tear (up to 0.3 mm) and to impart special physical and mechanical properties of the manufactured machine parts surfaces.

Abstract: Joining materials by forming is an interesting approach to the manufacture of hybrid (multi material) parts. By establishing a cold pressure weld between metallic surfaces, high quality joints with superior properties can be achieved. Reliable cold welding conditions are difficult to set up, however, since the weld initiation requires extraordinary clean, virtually sheer surfaces. Until today such conditions could only be achieved under a high vacuum conditions. Various studies on cold pressure welding reported that under vacuum welds can be established at significantly lower deformation than in a normal atmosphere. Since adverse deformation is currently needed in industrial cold pressure welding processes like the cold roll cladding of metal bands, a new process with in-line electrochemical surface treatment, is investigated. The ECUF process is intended to supply clean and thereby highly activated surfaces to the cold pressure welding process.This paper presents first results on the weld-ability of copper specimens with regard to the influence of the welding environment: air, argon and KCl solution. Butt welds were made by pressure welding of previously fractured specimens.

Abstract: Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) studied the interaction of argon ions with a natural oxide layer of polycrystalline aluminum. It was found that the bombardment of argon ions with an energy lower sputtering threshold Al₂O₃ leads to accumulation of ions bombarding the interstitial voids in the surface, thereby forming a solid solution of atoms of the target, the argon ions and nitrogen ion beam, the captured residual gas from the chamber of the spectrometer.

Abstract: The existence of gases in the solid metals (hydrogen and nitrogen) assumes the presence of these gases in metals even before solidification, respectively in the elaboration, secondary treatment and casting phases. Usually, great amounts of gases dissolved in steels can be detected, between 3.5-8ppm for hydrogen and 0.02-0.03% for nitrogen, respectively. There are also cases when the purpose is to alloy with nitrogen, this being the case of austenitic stainless steels where the nitrogen content can reach 0.5% using ferrochromium or ferromanganese alloyed with nitrogen in 3-5.5 %. The main method of removing these gases is bubbling with inert gases and /or treating the steel in a vacuum facility. The paper presents a study regarding increasing the removal efficiency of nitrogen from the liquid steel by changing the bubbling parameters (flow, pressure, duration) but also the basicity of the refining slag. The equations of the regression surface and the identified fields are of a real help for the technologists, allowing quick decisions but they are also important for the quality of the metallic products [.

Abstract: In this paper, we have developed an empirical formula describing the equation of state of argon fluid using cluster expansion technique and commonly used force parameters. To test the reliability of the formula, we have further simulated the equation of state for argon at corresponding states employing molecular dynamic method. The comparisons have shown that the empirical formula gives much better prediction than that from the simple form equation of ideal gases and the inclusion of the third virial terms in expansions is prominently important.

Abstract: Metal injection molding (MIM) is capable of mass producing intricately shaped components. In recent years, this technology has been adopted in the electronic, computer, aerospace and medical industries. Titanium alloy (Ti6Al4V) is difficult to process because of its reactive nature and primarily because of problems with carbon and oxygen impurities. Even at low concentration, these interstitials can severely degrade the mechanical properties of titanium and its alloys. The main objective of this study is to develop a sintering condition that would eliminate problems with carbon and oxygen contamination and facilitate binder removal, thus enhance the sintering properties. Ti6Al4V with binder formulation consists of polyethylene (PE), paraffin wax (PW), stearic acid (SA) and palm oil derivatives; palm stearin (PS) were mixed homogeneously and injected to produce green compacts. The binders then were removed and sintering of injection molded material was conducted up to 1200 °C in vacuum atmosphere. The parts sintered at 1150 °C for 8 h exhibited among the highest tensile strength of 921.1 MPa while the elongation, density, porosity and hardness was 6.4%, 4.358 g/cm³, 3.16% and 320 HV respectively. This is the advantageous of additional argon flow during debinding , whereas the physical and mechanical properties were improved due to the impurity gas in argon that had strong effects on the aspects of densification and elimination of pores that turn the powder into a dense solid Ti6Al4V.

Abstract: Metal Injection Moulding (MIM) is an efficient method for high volume production of complex shape components from powders. The purpose of this study is to determine the sintering condition of titanium alloy (Ti6Al4V) tensile shape sample. In high temperature, Ti6Al4V will react with oxygen to form of titanium oxide (TiO₂) which present a problem during sintering thus affected the mechanical properties and microstructure. This reaction can be avoided either by introducing argon gases or in vacuum condition. Ti6Al4V with binder formulation consist of polyethylene (PE), paraffin wax (PW), stearic acid (SA) and palm oil derivatives; palm stearin (PS) were mixed homogenously and injected to produce green compact. The binders then are removed and sintered at 1100 °C for 8 h. During sintering, the debound part is heated, thus allowing densification of the powder into a dense solid with the elimination of pores. It was expected that the impurity gas in argon had strong effects on aspects of the densification and properties. Samples of PE/PS formulation with argon added to the sintering atmosphere, experience density of 4.375g/cm₃ and tensile strength stated at 1000.100MPa compared to samples in vacuum condition which do not show any significant increment with density of 3.943g/cm₃ and tensile strength at 325.976MPa. PE/PW/SA samples of vacuum condition also show no improvement in sintered properties. However with additional argon flow the density can reach until 4.359g /cm₃ and 940.823MPa of tensile strength. Ti-alloy sintered in argon exhibited better densification rate than in vacuum with high strength, better elongation and lower porosity. In argon, the powder particles became interconnected signifying densification was achieved due of non-reactive properties of inert gases that prevent undesirable chemical reactions from taking place.