Determination of Adhesive and Cohesive Strength in Metal Coatings Deposited by Hypersonic Metallization

. It is known that at present, methods of thermal spraying are widely used to restore and strengthen various worn-out machine parts. As a rule, metal coatings applied by thermal spraying have lower strength characteristics than solid materials. It is believed that the strength of coatings is proportional to their adhesive and cohesive strength. The value of adhesive and cohesive strength depends on various factors, including the nature of the materials and the technology of coating. An important factor characterizing the possibility of using metal coatings in various industries is the strength of adhesion of coatings to the base metal. The paper presents the determination of the adhesive and cohesive strength of coatings from different materials, applied by the method of hypersonic metallization. The results of testing the strength of metal coatings made of ER316LSi-grade wire, nichrome (Cr20Ni80) and molybdenum wire are given in the paper. Based on the results of metallographic studies, the proportion of the participation of cohesive and adhesive components in the strength of coatings has been determined, and some features of coating destruction have been described. It has been found that the participation of the cohesive and adhesive components of the coating strength differs depending on the material used. The cohesive component prevails in the strength of coatings made of high-alloy wire of the ER316LSi-grade, at which destruction mainly occurs along the coating-base boundary. For nichrome coatings and especially for coatings made of molybdenum, the cohesive component is predominant, in which the destruction of the coating occurs not along the coating-base boundary, but between the coating layers.

Experimental Investigations on Eco-Friendly Helium-Mist Near-Dry Wire-Cut EDM of M2-HSS Material

In this paper, helium-assisted near-dry wire-cut electrical discharge machining (NDWEDM) method molybdenum wire has been used to reduce the environmental impact and to cut M2-HSS material. The pressurized non-reacting helium gas mixed with a small amount of water (Helium-mist) is used as the dielectric fluid to accomplish adequate cooling and flush-out debris. The new experimental setup has been developed to conduct the near-dry WEDM tests using the L9 orthogonal array of the Taguchi technique. The input parameters such as voltage (V), pulse-width (PW), pulse-interval (PI), and flow rate (F) of mixing water and output variables are the material removal rate (MRR) and surface roughness (Ra). It was observed that MRR and Ra are amplified by the rise in voltage and pulse-width, and flow rate conversely, the pulse interval minimizes the responses. The percentage of contribution of pulse width, voltage, pulse interval and flow rate are 24.06%, 32.98%, 12.75% and 30.21% on MRR and 20.94%, 22.22%, 47.86% and 8.97% on Ra respectively. Finally, the confirmation trials have been accomplished to validate the foreseen best parameter sets on optimal responses.

On the phenomena of partial crystallization of highly undercooled magnesium silicate molten droplets

The present work reports real-time observations of the phenomena of partial crystallization of one of the glass-forming materials, namely enstatite (MgSiO3) from its supercooled liquid droplet. Initially, the molten droplet has been held under purely non-contact conditions using the aerodynamic levitation technique. The desired levels of undercooling have been achieved by deliberately making the levitated molten droplet touch a thin molybdenum wire and hence to initiate heterogeneous nucleation from the point of contact. Influence of thermal parameters like undercooling, cooling rates and recalescence on the process of crystallization is investigated. To understand and report the morphological properties and extent of crystallinity, the solidified enstatite samples have been characterized using optical/scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively, which confirmed the formation of partially crystallized enstatite spherules and fully glass spherules. XRD showed sharp peaks of enstatite, which confirm crystallinity and a halo profile confirms the amorphous phase of enstatite. Based on the observations of several experiments, we propose the effect of thermal parameters such as levels of undercooling and recalescence on the partial crystallization, as well as partial glass formation from the initially molten droplets of enstatite composition.

Performance Evaluation of SiC Powder Mixed Electrical Discharge Machining: A Case of Wire Cut Mode with Re-Circulating Molybdenum Wire

Review of the available literature on powder mixed electrical discharge machining (PMEDM) indicates, that most of the research has been done for “die sinking machining mode” whereas the “wire cut machining mode” has not received due attention despite being an important process variant. This work employs Silicon Carbide (SiC) powder mixed dielectric fluid for machining of AISI D2 in “wire cut” mode with re-circulating molybdenum wire (an economic and chemically stable proposition as tool). The effect of five process parameters (powder concentration, peak current, pulse on time, nozzle flushing pressure and stand-off distance) have been evaluated on surface roughness, kerf width, material removal rate and wire wear ratio using Taguchi’s approach. It is found that for surface roughness, higher current and low to moderate concentration levels (2 to 4g/l) deteriorate surface quality; higher values of pressure and stand-off distance are also seen to adversely affect it. For material removal rate, pulse on time as well as its interactions with powder concentration and current, are statistically significant. A higher pulse on with smaller and moderate powder concentrations (2g/l and 4g/l) reduces MRR. For wire wear ratio, current is the sole significant factor (PCR of ~ 65%). SEM analysis of the machined workpiece for the maximum MRR condition quantifies recast layer as ~ 19microns. An indirect comparison with the reported values for non-powdered EDM process indicates that for the similar wire (molybdenum), the use of SiC powder maintains the surface roughness and kerf values, for a much harder D2 material used in this work.

A Study on the Manufacturing of Molybdenum Pins for Electrodes

The molybdenum cup and molybdenum pin, which are the main materials of the molybdenum electrode used for the LCD BLU CCFL electrode, have not been developed in Korea and imported from Japan. In this paper, especially, research on prototype manufacturing and CAE analysis is performed to develop a molybdenum pin. In this research, to develop the manufacturing technology of molybdenum pin used for CCFL electrode of LCD BLU, development of linear processing technology, development of molybdenum wire surface treatment technology, development of wire cutting technology, production of molybdenum pin, design and fabrication of JIG and Fixture for inspection, molybdenum pin prototyping and analysis, and development of 100% molybdenum pin inspection technology. The development of molybdenum pins developed through this research can overcome Japan's technological level, which depends entirely on imports from Japan, and it is thought that the development will have a significant impact on the overall industry using molybdenum pins.