The ω phase formation during laser cladding and remelting of quasicrystal forming AlCuFe on pure aluminum

We report the formation ω phase in the remelted layers during laser cladding and remelting of quasicrystal forming Al65Cu23.3Fe11.7 alloy on pure aluminum. The ω phase is absent in the clad layers. In the remelted layer, the phase nucleates at the periphery of the primary icosahedral phase particles. A large number of ω phase particles forms enveloping the icosahedral phase growing into aluminum rich melt, which solidify as υ-Al solid solution. On the other side it develops an interface with aluminum. A detailed transmission electron microscopic analysis shows that ω phase exhibits orientation relationship with icosahedral phase. The composition analysis performed using energy dispersive x-ray analyzer suggests that this phase has composition higher aluminum than the icosahedral phase. The analysis of the available phase diagram information indicates that the present results represent large departure from equilibrium conditions. A possible scenario of the evolution of the ω phase has been suggested

Laser cladding of quasi-crystal-forming Al-Cu-Fe-Bi on an Al-Si alloy substrate

We report here the results of an investigation aimed at producing coatings containing phases closely related to the quasi-crystalline phase with dispersions of soft Bi particles using an Al-Cu-Fe-Bi elemental powder mixture on Al-10.5 at. pct Si substrates. A two-step process of cladding followed by remelting is used to fine-tune the alloying, phase distribution, and microstructure. A powder mix Al64CU22.3Fe11.7Bi2 of has been used to form the clads. The basic reason for choosing Bi lies in the fact that it is immiscible with each of the constituent elements. Therefore, it is expected that Bi will solidify in the form of dispersoids during the rapid solidification. A detailed microstructural analysis has been carried out by using the backscattered imaging mode in a scanning electron microscope (SEM) and transmission electron microscope (TEM). The microstructural features are described in terms of layers of different phases. Contrary to our expectation, the quasi-crystalline phase could not form on the Al-Sisubstrate. The bottom of the clad and remelted layers shows there growth of aluminum. The formation of phases such as blocky hexagonal Al-Fe-Si and a ternary eutectic (Al + CuAl2 + Si) have been found in this layer. The middle layer shows the formation of long plate-shaped Al13Fe4 along with hexagonal Al-Fe-Si phase growing at the periphery of the former. The formation of metastable Al-Al6Fe eutectic has also been found in this layer. The top layer, in the case of the as-clad track, shows the presence of plate-shaped Al13Fe4along with a 1/1 cubicrational approximant of a quasi-crystal. The top layer of the remelted track shows the presence of a significant amount of a 1/1 cubicrational approximant. In addition, the as-clad and remelted microstructures show a fine-scale dispersion of Bi particles of different sizes formed during monotectic solidification. The remelting is found to have a strong effect on the size and distribution of Bi particles. The dry-sliding wear properties of the samples show the improvement of wear properties for Bi-containing clads. The best tribological properties are observed in the as-clad state, and remelting deteriorates the wear properties. The low coefficient offriction of the as-clad and remelted track is due to the presence of approximant phases. There is evidence of severe subsurface deformation during the wear process leading to cracking of hard phases and a change in the size and shape of soft Bi particles. Using these observations,we have rationalized possible wear mechanisms in the Bi-containing surface-alloyed layers

Studies on laser surface melting of Al-11% Si alloy

In the present investigation the effect of laser surface melting on wear and corrosion resistance of Al-11 wt.% Si alloy has been investigated. Laser surface melting has been carried out using a 2 kW continuous wave CO2 laser at an applied power of 2.3 kW and scan speed ranging from 6 to 12 mm/min. Following the laser surface melting, a detailed investigation of the melted zone in terms of microstructure, composition and phases were undertaken. Mechanical properties of the melted zone were evaluated so far as the microhardness and wear resistance were concerned. The corro-sion behaviour of the as-received and the laser surface melted surface was evaluated in 1(M) H2SO4, 1(M) HNO3 and 3.56 wt.% NaCl solutions. The microstructure of the melt zone consists of grain refinedAl andAl-Si eutec-tic colonies which results in an improved microhardness from 87 VHN as compared to 55 VHN of the as-received Al-Si alloy. The wear resistance of the melt surface was improved significantly as compared to the as-received Al-Si alloy. A detailed corrosion study in various environments showed that corrosion resistance was marginally less in the 3.56 wt.% NaCl and 1 M H2SO4 solutions, but was better in the 1 M HNO3 solution

Laser composite surfacing of a magnesium alloy with chromium carbide

The present study concerns improving the wear resistance of a Mg alloy (MEZ) by melting the surface with a high power laser and simultaneously injecting hard particles, of Cr2C3 +(25mm -40mm) into the surface. The laser processing was carried out using a continuous wave CO2 laser, Model: Rofin Sinar, RS 10000, with a beam diameter of 4 mm and a focal point 30 mm above the surface. Following laser processing, a detailed investigation of the microstructures, compositions and phases were undertaken and mechanical (wear resistance) and electrochemical (pitting corrosion resistance) properties of the surface layer were evaluated in details. The microstructure of the surface layer consists of uniformly dispersed Cr2C3 precipitates in grain-refined matrix. The micro-hardness and wear resistance of the surface layer were significantly improved as compared to the base metal

Laser surface cladding of EN19 steel with stellite 6 for improved wear resistance

The present study concerns the generation of a wear resistant Stellite 6 CO2 laser clad layer on the surface of an EN19 steel substrate by means of laser surface cladding. Laser surface cladding was carried out by melting the Stellite powder (particle size 10 to 40 μm) supplied through a pneumatically driven powder delivery system (using a 4 MP powder unit) with a 9 kW continuous wave (CW) CO2 laser with the wavelength 10.6 µm. The microstructure of the clad layer was found to consist of three zones: a clad layer comprised of dendrites of Stellite 6; an alloyed zone comprised of a cellular microstructure, which was a mixture of Fe and Co; and the heat affected zone (HAZ), which was a mixture of pearlite and martensite. Compared to the EN19 steel substrate, the micro-hardness of the clad layer represented a significant improvement, increasing to 1200 VHN

Effect of interlayer configurations on joint formation in TLP bonding of Ti-6Al-4V to Mg-AZ31

YesIn this research work, the transient liquid phase (TLP) bonding process was utilized to fabricate joints using thin (20μm) nickel and copper foils placed between two bonding surfaces to help facilitate joint formation. Two joint configurations were investigated, first, Ti- 6Al-4V/CuNi/Mg-AZ31 and second, Ti-6Al-4V/NiCu/Mg-AZ31. The effect of bonding time on microstructural developments across the joint and the changes in mechanical properties were studied as a function of bonding temperature and pressure. The bonded specimens were examined by metallographic analysis, scanning electron microscopy (SEM), and X-ray diffraction (XRD). In both cases, intermetallic phase of CuMg2 and Mg3AlNi2 was observed inside the joint region. The results show that joint shear strengths for the Ti-6Al-4V/CuNi/Mg- AZ31 setup produce joints with shear strength of 57 MPa compared to 27MPa for joints made using the Ti-6Al-4V/NiCu/Mg-AZ31 layer arrangement.NSERC (Canada

Evaluation of the possibility of using diatomite natural mineral as a composite agent in acrylic coating

WOS: 000427736200014In the present study the possibility of the commercially available acryl and diatomite earth (DE) mineral as a composite coating for corrosion protection of Mg alloys has been evaluated. The acrylic coating is used as a top coating in a wide field of applications like automotive, aerospace, medicine and electronics where it shows beneficial properties. Diatomite-dispersed acrylic paint was applied over the substrate by conventional spray technique with an air pressure of 3 kg cm(-2). Firstly the acryl was mixed with hardener and then the DE was added to the mixture. Four types of coating with 0, 2, 4, 8 g/L DE have been prepared. The results show that adding up to 4 g/L of the DE improved the corrosion resistance and produced a coating with acceptable surface roughness