Papers by Author: Viorel Aurel Şerban

Abstract: This study presents investigations regarding processing X2CrNi18-9 stainless steel sheet with 2 mm thickness using abrasive waterjet cutting.By variation of base technological parameters (water pressure, travelling speed, abrasive rate and focusing tube inner diameter) the shape together with size of the kerf were analyzed.Roughness measurements from the entrance to exit of cut surfaces in correlation with the analysis carried out using an optical microscope highlights work hardening of the marginal layer. This phenomenon is less accentuated in the higher area which is in the vicinity of the focusing tube and intensifies towards the lower area of cut material.

Abstract: In this paper research elements regarding the effect of water pressure variation on cut surfaces quality are presented in the field of abrasive water jet cutting of materials hard to process by machining such as austenitic stainless steels, in this case with a thickness of 20 mm. Selection of the optimal cutting process based on technical and economic criteria takes into consideration the type and thickness of the targeted material and also the physical and geometrical quality requirements. The present paper contains experimental research results regarding abrasive water jet cutting of austenitic stainless steel EN 1.4306 (ASTM 304 L) at different values of water pressure. The abrasive material used is Garnet with particle granulation 80 Mesh. By making roughness measurements and hardness examinations of the cut surface an evaluation will be made of the surface quality defining the optimal pressure values.

Abstract: Components soldered with Sn-based alloys are susceptible to the growth of whiskers. Tin whiskers have been proven to be responsible for equipment failures in a wide range of industries. In order to reduce defects in electronic components a new solder alloy is proposed based on the Sn-Cu alloys. The Sn-Cu-Ga alloy utilised in this study was fabricated as a ribbons using melt-spinning method. These ribbons were then soldered onto electroplated tin layers. Preliminary characterization of the solder alloy is presented in this paper, including scanning electron microscopy, EDX mapping and X-ray diffraction. Key words: tin whiskers, PCB, printed circuit boards, melt spinning, solder, ribbons

Abstract: Development of Fe-based bulk metallic glasses (BMG) with good mechanical and soft magnetic properties has become a major objective in the materials science field. Bulk metallic glasses present an interesting combination of properties. They exhibit very high strength (both in tension and compression), large elastic elongation limit, high hardness, excellent corrosion resistance, and good soft magnetic properties. These properties makes them suitable for many applications like high resistant control cables, pressure vessels, micro-components, pressure sensors, microgears for motors, magnetic cores for power supplies and hard fibers in composite materials. Multi-component Fe₆₀Co₁₄Ga₂P₁₀B₅Si₃Al₃C₃ bulk metallic glass was synthesized in rod form with a diameter of 1 mm by copper mould casting technique using raw industrial materials. The obtained alloy was analyzed by X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM) techniques, in order to determine the phase constituent, the thermal stability and the fracture surfaces of as-cast samples. The mechanical behaviour was investigated by microhardness and compression tests. The values recorded for hardness and fracture strength includes this alloy in the category of high resistant materials.

Abstract: The current study is focused on deposition of different carbide based powders as WC/10Co/4Cr, Cr3C2/25NiCr, CrC/37WC/18M using High Velocity Oxygen Fuel (HVOF) spraying technique onto the surface of low carbon steel substrates. The obtained coatings were characterized by means of X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) to study their phases and morphology. Hardness and porosity values of the coatings were also measured. The sliding wear behavior was evaluated using the pin-on-disk method and the corrosion resistance was determined by open cell potential measurements and salt spray tests. Comparative results of the investigated samples showed that the WC/10Co/4Cr coating had the best wear properties and the Cr3C2/25NiCr coating had the best corrosion resistance.

Abstract: Ni based amorphous alloys with Si and B, which can also, contains Fe and Cr, prepared by rapid solidification, have low melting temperatures. This fact increases their susceptibility to be joined by welding and brazing. The glass forming ability (GFA) is conditioned also by the crystallization delay, due to certain chemical composition of the alloys. The thermal stability of these alloys was revealed by DTA analysis and structural characteristics were investigated by XRD. Applying an annealing at temperatures between 420°C and 540°C, with 30 minutes maintaining time, allowed the investigation of phase occurred during the crystallization and the estimation of the crystalline grains dimensions.

Abstract: Nickel based amorphous alloys have been developed in ribbons form by planar flow casting method and were subjected to tensile tests. For this purpose, specimens with calibrated area were obtained by electroerosion cutting method and tested at tensile test with different strain rates. Following the results obtained during the tests, the mechanical properties have been determined and compared and the fracture behaviour has been analyzed by scanning electron microscopy.

Abstract: The paper presents a study regarding the evaluation of the adherence strength using scratch test of WC 12%Co coating deposited by high velocity oxygen fuel (HVOF) method onto the surface of a carbon steel substrate.The coating morphology was characterized by scanning electron microscopy (SEM).The scratching process of the WC Co coating was controlled and monitored using a Millennium 200 Technical Tribo equipment, the test being performed according to DIN EN 1071-3 Standard. The load required to cause the failure of the WC Co coating on the carbon steel substrate was determined. The points where the coating fails by cracking are taken as critical failure points.

Abstract: Nickel–titanium- group 5A metal (V, Nb, Ta, Zr) alloys are known as promising hydrogen-selective membrane materials. They can potentially be used in membrane reactors, which can produce high-purity H₂ and CO₂ streams from coal-derived syngas at elevated temperatures. The master alloys were prepared by arc melting using high purity metals in a Ti-gettered argon atmosphere. The alloys were melted several times in order to improve homogeneity. The ingots were induction-melted under a high-purity argon atmosphere in a quartz tube and graphite crucible injected through a nozzle onto a Cu wheel to produce rapidly solidified amorphous ribbons. Thermal stability of the Ni40Ti40Nb20 and Ni32Ti48Nb20 thin tapes has been examined using DTA analysis.

Abstract: The aim of the work was to study the microstructure and wear properties of fine-structured HVOF and HVAF sprayed WC-10Co-4Cr coatings prepared from powder having submicron-sized tungsten carbides. The coatings were deposited by HVOF (High Velocity Oxygen Fuel) and HVAF (High Velocity Air Fuel) using propane as a fuel gas in both processes, and using oxygen or air as oxidizing gas for combustion, respectively. Nitrogen was used as carrier gas for the powder. Commercially available agglomerated and sintered cermet powder with main carbide sizes under 500 nm was used in this study. Scanning electron microscopy (SEM) and X-ray diffraction were performed in order to characterize the powder and the microstructures formed during the spraying processes. The microhardness HV0.3 of the coatings was investigated and the pin on disk test was used to determine the sliding wear behaviour. The rubber wheel abrasion test was performed in order to determine the abrasion wear resistance of the coatings.