Microstructure and properties of BN/Ni-Cu composites fabricated by powder technology

Microsize Powders of Ni and Cu were prepared by water atomization technique to fabricate metal matrix composites containing various percentages of nanosized boron nitride particles (1, 2, 3, 4, 5 wt. % of BN in a matrix containing (20 wt. %Ni and 80 wt. %Cu). The prepared mixtures were cold compacted under 400 MPa, and sintered for 2 h at 1000 °C in a controlled atmosphere of 3:2 N2/H2 gas mixtures. The microstructure and the chemical composition of the prepared powders as well as the consolidated composites were investigated by X-ray diffraction as well as field emission scanning electron microscope (FESEM) equipped with an energy dispersive spectrometer (EDS). The produced Cu and Ni powders have spheroid shape of size less than 100 microns, but the investigated BN has an equiaxed particle shape and particle size of ∼ 500 nm. It has been also observed that BN and Ni particles were homogeneously distributed in the Cu matrix of the present BN/Ni-Cu composites. The density, electrical resistivity, saturation magnetization and hardness of the composites were measured. It was observed that, by increasing BN content, the relative density was decreased, while the saturation magnetization, electrical resistivity and hardness were increased

Effect of Welding Variables on the Quality of Weldments

The effect of nitrogen addition, heat input, and filler metals on weld metal microstructure and mechanical properties of alloy 316 ASS are studied. Autogenous gas tungsten arc welding (GTAW) is employed by adding up to 2vol. % N2 in Ar. These variables affect a number of welding aspects, including arc characteristics and microstructure. The influence of shielding gas mixtures on microstructure and mechanical properties of GTAW of austenitic 316 stainless steel is studied. Mechanical properties of welds are determined through uniaxial tension, hardness measurements, impact, and bending tests. Weld defects, as porosity and inclusions are examined using radiographic testing. Weld specimens are free of porosity, inclusions, and hydrogen cracking. Mechanical properties and cooling rate are lower at higher heat input, but the cooling time, nugget area, and solidification time are higher. The addition of N2 to Ar shielding gas leads to higher values of the ultimate tensile strength ‘UTS’, yield stress ‘YS’, and elongation percent. UTS, YS, and elongation of welds depend on heat input, filler metal, and N2 content of shielding gas. Finally, a mathematical model is built depending upon the welding current, filler metals, and shielding gases

An analytical model of heat generation for eccentric cylindrical pin in friction stir welding

An analytical model for heat generation for eccentric cylindrical pin in friction stir welding was developed that utilizes a new factor based on the tool pin eccentricity. The proposed analytical expression is a modification of previous analytical models from the literature, which is verified and well matches with the model developed by previous researchers. Results of plunge force and peak temperature were used to validate the current proposed model. The cylindrical tool pin with eccentricities of 0, 0.2, and 0.8 mm were used to weld two types of aluminum alloys; a low deformation resistant AA1050-H12, and a relatively high deformation resistant AA5754-H24 alloy. The FSW was performed at constant tool rotation speed of 600 rpm and different welding speeds of 100, 300, and 500 mm/min. Experimental results implied that less temperature is generated using eccentric cylindrical pin than cylindrical pin without eccentricity under the given set of FSW process conditions. Furthermore, numerical simulation results show that increasing the pin eccentricity leads to decrease in peak temperature

Bobbin Tool Friction Stir Welding of Aluminum Using Different Tool Pin Geometries: Mathematical Models for the Heat Generation

In this work, three mathematical models for the heat generation during bobbin tool friction stir welding (BT-FSW) of aluminum using three tool pin geometries have been proposed. The models have utilized and updated the available models for the heat generation during the conventional tool friction stir welding (CT-FSW). For the validation of the models, BT-FSW experiments have been carried out for aluminum alloy AA1050 using three different pin geometries (cylindrical, square, and triangular), at different welding speeds of 200, 400, 600, 800, and 1000 mm/min and a constant tool rotation speed of 600 rpm. The welding temperatures during BT-FSW have been measured to be compared with that calculated from the models at the same parameters. It has been found that the calculated welding temperatures from the models and that measured during BT-FSW are in good agreement at all the investigated welding speeds especially in case of the square and cylindrical pins, proving the validity of the developed models for the predication of the heat generation as well as the welding temperatures. This will allow proper designing of the BT-FSW parameters and avoiding the conditions that can deteriorate the joint quality and properties

Effect of Copper Addition on the AlCoCrFeNi High Entropy Alloys Properties via the Electroless Plating and Powder Metallurgy Technique

To improve the AlCoCrFeNi high entropy alloys’ (HEAs’) toughness, it was coated with different amounts of Cu then fabricated by the powder metallurgy technique. Mechanical alloying of equiatomic AlCoCrFeNi HEAs for 25 h preceded the coating process. The established powder samples were sintered at different temperatures in a vacuum furnace. The HEAs samples sintered at 950 °C exhibit the highest relative density. The AlCoCrFeNi HEAs model sample was not successfully produced by the applied method due to the low melting point of aluminum. The Al element’s problem disappeared due to encapsulating it with a copper layer during the coating process. Because the atomic radius of the copper metal (0.1278 nm) is less than the atomic radius of the aluminum metal (0.1431 nm) and nearly equal to the rest of the other elements (Co, Cr, Fe, and Ni), the crystal size powder and fabricated samples decreased by increasing the content of the Cu wt%. On the other hand, the lattice strain increased. The microstructure revealed that the complete diffusion between the different elements to form high entropy alloy material was not achieved. A dramatic decrease in the produced samples’ hardness was observed where it decreased from 403 HV at 5 wt% Cu to 191 HV at 20 wt% Cu. On the contrary, the compressive strength increased from 400.034 MPa at 5 wt% Cu to 599.527 MPa at 15 wt% Cu with a 49.86% increment. This increment in the compressive strength may be due to precipitating the copper metal on the particles’ surface in the nano-size, reducing the dislocations’ motion, increasing the stiffness of produced materials. The formability and toughness of the fabricated materials improved by increasing the copper’s content. The thermal expansion has increased gradually by increasing the Cu wt%

Improvement ductility and corrosion resistance of CoCrFeNi and AlCoCrFeNi HEAs by electroless copper technique

In this study, the effect of copper coated particles on the properties of CoCrFeNi and AlCoCrFeNi high entropy alloys (HEAs) was studied. Mechanical milling is applied to achieve a good homogeneous distribution of an equiatomic CoCrFeNi and AlCoCrFeNi HEAs for 25 h milling time, followed by an electroless copper plating with 5–20 wt.% Cu by 5 wt.%, have been established. The prepared powder alloys were compacted at 800 MPa, then sintered at 1150 °C, 1200 °C, 1250 °C for Cux/(CoCrFeNi)1-x HEA and 900 °C, 950 °C, and 1000 °C for Cux/(AlCoCrFeNi)1-x HEA in a vacuum furnace for 90 min. The correlation between the microstructure, density, hardness, wear behavior and corrosion resistance of the fabricated CoCrFeNi, Cux/(CoCrFeNi)1-x and Cux/(AlCoCrFeNi)1-x HEAs were investigated. The results revealed that, alloys which sintered at 1200 °C for (CoCrFeNi – Cux/(CoCrFeNi)1-x HEAs) and at 950 °C for (Cux/(AlCoCrFeNi)1-x HEA) exhibit the highest relative density. Densification was enhanced as a result of increasing the nano Cu wt.% content. A dramatic decrease in the produced samples’ hardness was observed where it decreased from 189.1 HV to 134.5 HV for Cux/(CoCrFeNi)1-x and from 403 HV to 191 HV for Cux/(AlCoCrFeNi)1-x HEAs by the addition of the nano Cu wt.% content. In addition, Wear rate is increased gradually by the addition of the nano Cu wt.% content. The electrochemical results indicate that an increased nano Cu wt.% content corresponds to an increased corrosion rate from 0.297 mm/year to 1.84 mm/year for Cux/(CoCrFeNi)1-x and from 0.03 mm/year to 0.093 mm/year for Cux/(AlCoCrFeNi)1-x HEAs

Bobbin Tool Friction Stir Welding of Aluminum Thick Lap Joints: Effect of Process Parameters on Temperature Distribution and Joints’ Properties

Bobbin tool friction stir welding (BT-FSW) is characterized by a fully penetrated pin and double-sided shoulder that promote symmetrical solid-state joints. However, control of the processing parameters to obtain defect-free thick lap joints is still difficult and needs more effort. In this study, the BT-FSW process was used to produce 10 mm AA1050-H14 similar lap joints. A newly designed bobbin tool (BT) with three different pin geometries (cylindrical, square, and triangular) and concave shoulders profile was designed, manufactured, and applied to produce the Al alloy lap joints. The experiments were carried out at a constant tool rotation speed of 600 rpm and a wide range of various welding travel speeds of 200, 400, 600, 800, and 1000 mm/min. The generated temperature during the BT-FSW process was recorded and analyzed at the joints’ center line, and at both advancing and retreating sides. Visual inspection, macrostructures, hardness, and tensile properties were investigated. The fracture surfaces after tensile testing were also examined. The results showed that the pin geometry and travel speed are considered the most important controlling parameters in BT-FSW thick lap joints. The square (Sq) pin geometry gives the highest BT-FSW stir zone temperature compared to the other two pins, cylindrical (Cy) and triangular (Tr), whereas the Tr pin gives the lowest stir zone temperature at all applied travel speeds from 200 to 1000 mm/min. Furthermore, the temperature along the lap joints decreased with increasing the welding speed, and the maximum temperature of 380 °C was obtained at the lowest travel speed of 200 mm/min with applying Sq pin geometry. The temperature at the advancing side (AS) was higher than that at the retreating side (RS) by around 20 °C. Defect-free welds were produced using a bobbin tool with Cy and Sq pin geometries at all the travel welding speeds investigated. BT-FSW at a travel speed of 200 mm/min leads to the highest tensile shear properties, in the case of using the Sq pin. The hardness profiles showed a significant effect for both the tool pin geometry and the welding speed, whereas the width of the softened region is reduced dramatically with increasing the welding speed and using the triangular pin