INVESTIGATION OF WAYS TO REMOVE OXIDE FILM FROM THE SURFACE OF METALS AND SOLDER MATERIALS IN THE SOLDERING PROCESS UNDER DIFFERENT CONDITIONS

The article considers important to study the issues of removal of oxide films from the surface of metals and solder materials and the increase of homogeneity of the space in the process of soldering under the active gas and vacuum conditions. Theoretical and experimental studies have shown that the process of self-fluxing is mainly associated with the reduction of adsorption forces, dispersion of oxide films and solubility in solder. Keywords: steel unit, copper-phosphorus alloy, active gas-vacuum, melting temperature, cracking, wetting, oxide film, self-fluxing, microstructure, hardening.

Effect of minor Nb on isothermal-oxidation and hot corrosion behavior of two Nickel-based superalloys under Na2SO4 / Na2SO4-NaCl

Two nickel-based superalloys with and without minor Nb were prepared using double vacuum melting. The comparison of microstructure, isothermal-oxidation and hot corrosion behavior under molten Na2SO4 / Na2SO4+25wt. % NaCl at 900 C was evaluated. Results indicated that Nb accelerated the formation of chromia scale in a short transient stage, leading to a lower scaling rate. Nb also inhibited the internal oxidation/ nitridation. Both significantly improved the hot corrosion resistance under Na2SO4. However, the beneficial effect of Nb is slight under mixed salts with NaCl. The beneficial effects of Nb on oxidation and hot corrosion are discussed in detail.

Evolution of Non-metallic Inclusions Through Processing in Ti-V Microalloyed 316L and Al-V Microalloyed 17-4PH Stainless Steels for Hipping Applications

Powders produced by air-melted gas atomization (AMGA) and vacuum induction gas atomization (VIGA) from Ti-V microalloyed 316L and Al-V microalloyed 17-4PH stainless steels along with their feedstock material and Hot Isostatically Pressed (HIP’d) products have been examined. Inclusion characteristics and development through process along with changes in grain size have been characterized. The main findings are that a thin oxide film forms on the powder surface, thicker for the 316L powder than the 17-4PH powder as indicated by XPS analysis of selected powder precursors, and large inclusions (predominantly oxides) are also observed on the 316L powder. This results in a high number of inclusions, including more complex two-phase inclusions, on the prior particle boundaries in the HIP’d material. Grain growth occurs during HIPping of the 316L powders with some evidence of inclusions locally pinning boundaries. In the vacuum-melted powder, smaller Ti-rich inclusions are present which give more grain boundary pinning than in the air-melted powder where Ti was lost from the material during melting. Consideration has also been made to determine the variation of Ti and V microalloying elements and residual Cu through processing. It was found that Ti was lost during air melting but partly retained after vacuum melting leading to the presence of fine and complex Ti-containing precipitates which provided grain boundary pinning during HIPping and heat treatment. V was retained in the melt by the use of both AMGA and VIGA processes, and therefore available for precipitation during HIPping. Residual Cu was retained during both air and vacuum melting and was associated with Mn S and Mn O S inclusions overwhelmingly outweighing that of Mn O inclusions in the two HIP’d 316L samples.

Study on Microstructure and Properties of Cu-14Fe-0.05C Alloy Prepared by Drawing

Cu-14Fe-0.05C alloy was prepared by using the vacuum melting process and then multipass drawing deformation was performed. The results showed that with rise of drawing strain, iron-rich phases in the Cu-14Fe-0.05C alloy gradually change from irregularly distributed coarse dendritic phases in the as-cast state to slender fibrous ones distributed parallel along the drawing direction. The higher the strain is, the slender and denser the fibers are and the more uniform the distribution is. Moreover, more interfaces are found between copper matrix and iron-rich phases and the hardness and resistivity of the alloy become higher.

Effect of Annealing on the Microstructure and Properties of Drawn Cu-14Fe-0.05C Alloy

Cu-14Fe-0.05C alloy was prepared by using the vacuum melting process and then multipass drawing deformation was performed. After that, the alloy in the as-drawn state was annealed. Based on this, the influence of annealing temperature on microstructure, mechanical performance and electrical conductivity of the alloy was studied. The results showed that the speed of recovery and recrystallization of the as-drawn Cu-14Fe-0.05C alloy accelerates and iron-rich fibers gradually become slender, bend and fracture, with the increase of annealing temperature. The tensile strength of the alloy constantly decreases, while elongation continuously rises and resistivity gradually reduces. With the extension of annealing time, tensile strength and resistivity of the Cu-14Fe-0.05C alloy gradually decreases, while elongation gradually increases.