The goals of this study were to investigate the fatigue limits of two Pd-Ag alloys (Ivoclar Vivadent) with differing mechanical properties and varying proportions of secondary alloying elements, examine the effect of casting porosity on fatigue behavior, and determine the effect of casting size on microstructures and Vickers hardness. The alloys selected were: IPS d.SIGN 59 (59.2Pd-27.9Ag-8.2Sn-2.7In-1.3Zn); and IS 64 (59.9Pd-26.0Ag-7.0Sn-2.8Au-1.8 Ga-1.5In-1.0Pt). Tension test bars, heat-treated to simulate dental porcelain application, were subjected to cyclic loading at 10 Hz, with R-ratio of -1 for amplitudes of compressive and tensile stress. Two replicate specimens were tested at each stress amplitude. Fracture surfaces were examined with a scanning electron microscope (SEM). Sectioned fatigue specimens and additional cast specimens simulating copings for a maxillary central incisor restoration were also examined with the SEM, and Vickers hardness was measured using 1 kg load. Casting porosity was evaluated in sectioned fatigue fracture specimens, using an image analysis program. The fatigue limit (2 × 10(6) loading cycles) of IS 64 was approximately 0.20 of its 0.2% yield strength, while the fatigue limit of d.SIGN 59 was approximately 0.25 of its 0.2% yield strength. These relatively low ratios of fatigue limit to 0.2% yield strength are similar to those found previously for high-palladium dental alloys, and are attributed to their complex microstructures and casting porosity. Complex fatigue fracture surfaces with striations were observed for both alloys. Substantial further decrease in the number of cycles for fatigue failure only occurred when the pore size and volume percentage became excessive. While the heat-treated alloys had equiaxed grains with precipitates, the microstructural homogenization resulting from simulated porcelain firing differed considerably for the coping and fatigue test specimens; the latter specimens had significantly higher values of Vickers hardness.
The study involves coating the high-speed steel (HSS) tool with cubic Boron via electroless nickel co-deposition. The surface coating of Ni-CBN was deposited via electroless nickel where the process of involved chemical reactions as the ceramic CBN powders was embedded within the layer. By introducing the electroless nickel process, the coating cost and procedure could be simplified. The electroless deposition has been extensively practised in industry, and the most prevalent coating offers excellent corrosion, wear and abrasion resistance, ductility, lubricity, electrical properties, and hardness. Thus, the introduction of the new electroless nickel (Ni-CBN) tools can be a contribution to the industry. This paper discussed on comparing the performance of Nickel-cubic boron nitride (Ni-CBN) HSS tool substrates and with uncoated HSS tool for its surface tolerance in milling of Aluminium Alloy 7075. The process variables selected during experimentation based on Taguchi L9 are cutting speed, feed rate, and depth of cut with three different levels for each parameter. Result shows, the lowest flank wear for coated measured is 51.34 μm while the highest is 380.26 μm. The highest surface roughness for uncoated is 1.154 μm and lowest 0.42μm. Meanwhile, for coated substrates, the highest Ra is 0.787μm and lowest 0.251μm. At the end of the analysis, the Ni-CBN HSS cutting tools are generally able to slightly reduce the tool wear with the longest tool lifetime 195 minutes compared uncoated 143 minutes. Therefore, it is concluded that the Ni-CBN HSS tool end mill are generally able to reduce the tool wear.
Nickel ceramic composite have emerged as potential corrosion, wear and thermal resistance. The present work contemplates reinforcement of Ni-P deposits with YSZ ceramic by electroless nickel deposition technique. The ratio of metal nickel (Ni) to ceramic yttria stabilized zirconia (YSZ) in composite materials determines its ability in corrosion, thermal, wear resistance. The amount of porosity enhances thermal insulation. The 2k full factorials design of experiment and analysis of variance (ANOVA) were used in screening the EN composite process parameters for effective Ni-YSZ co-deposition for high ceramic incorporation and porosity level. A mathematical model was developed using piecewise linear regression analysis to predict the composition and porosity in terms of the EN Ni-YSZ composite coating process parameters. The models developed to predict the Ni composition and porosity in Ni-P-YSZ composite.
The paper discusses the mechanical and physical behaviour of hybrid glass fibre reinforced plastic (GFRP). Hybrid GFRP was fabricated by three different types of glass fibre, namely, 3D, woven, and chopped, which were selected and combined with mixture of polyester resin and hardener. The hybrid GFRP was investigated by varying three parameters which were the composite volume fractions, hybrid GFRP arrangement, and single type fibre. The hybrid GFRP was fabricated by using open mould hand lay-up technique. Mechanical testing was conducted by tensile test for strength and stiffness whereas physical testing was performed using water absorption and hardness. These tests were carried out to determine the effect of mechanical and physical behaviour over the hybrid GFRP. The highest volume fraction of 0.5 gives the highest strength and stiffness of 73 MPa and 821 MPa, respectively. Varying hybrid fibre arrangement which is the arrangement of chopped-woven-3D-woven-chopped showed the best value in strength of 66.2 MPa. The stiffness is best at arrangement of woven-chopped-woven-chopped-woven at 690 MPa. This arrangement also showed the lowest water absorption of 4.5%. Comparing the single fibre type, woven had overtaken the others in terms of both mechanical and physical properties.
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