The effect of Si exposure height on the wear resistance of a hypereutectic Al-Si alloy was evaluated. The wear depth of the alloy was measured using a pin-on-disk type wear tester on the kinetic viscosity of lubricant, 2.20, 22.0 and 100 mm2/s. The Si exposure height was changed at each height of 0, 1.2, 2.4, 5.2, 7.5 μm by changing the immersing time in a NaOH solution. At the kinetic viscosity of 22.0 and 2.20 mm2/s of the lubricant, the wear curve shows a minimum value at the Si exposure height of 1.2 and 2.4 μm, resulting in a small effect of kinetic viscosity on the lubrication of the contact area.
We have developed scatter diagram method to evaluate material structure from the X-ray image data of electron probe micro analyzer (EPMA). The X-ray image data are projected on the two dimensional space of X-ray intensity to make a histogram so called scatter diagram. The analysis of this scatter diagram gives us important information of the material such as distribution of elements in complex compounds. We have applied this method for the study of the bonding interface between Ni-P electroless plate and SnPb solder. We have found the coarse δ (Ni3Sn4) phase and mixture fine (Ni3Sn4)x+Pb(1-x) phase at the bonding interface between Ni-P electroless plate and the Sn-Pb solder. The existence P-rich region at the edge of solder side in the Ni-P electroless plate is confirmed. The analysis of fracture surface revealed that the crack is generated at the interface between P-rich region and δ-phase and proceeds towards the solder.
In some cases, it is known that zinc doesn’t work as a sacrificed anode for preventing iron from corrosion. Electrochemical characteristics of an iron-zinc couple were studied in a 3 mass%NaCl solution under high oxygen pressures (0-2 MPa) and high temperatures (298-423 K). Reversal of polarity for coupling current between iron and zinc occurred under an oxygen pressure of 2 MPa and above 393 K. The period until the polarity reversal occurred, became shorter with increasing the temperature and with increasing the oxygen pressure. Before the polarity reversal occurred, galvanic corrosion potential of the iron-zinc couple was close to the corrosion potential of zinc anode. After the polarity reversal, the potential was close to the corrosion potential of iron anode. Polarization curves of iron before and after the polarity reversal were similar to each other. On the other hand, zinc corrosion potential shifted to nobler direction after the polarity reversal. X-ray diffraction analysis showed that zinc surface changed into ZnO. It was concluded that iron-zinc galvanic couple which acted as iron cathode and zinc anode was changed to the couple which acted as iron anode and zinc cathode due to the change of zinc to ZnO.
This study seeks to clarify the effects of gas contamination from milling atmospheres of mechanical alloying (MA) on mechanical properties. An iron-based dispersion alloy of Fe-13Cr-3W-0.5Ti-0.5Y2O3 (mass%) was selected as the experimental material. We prepared MA powders with the same composition as the dispersion alloy by milling mixed powders in various atmospheres such as argon, helium, hydrogen, nitrogen and vacuum, and then made bulk alloys by grooved rolling the MA powders. For the MA powders, we examined included atmospheric elements and their releasing processes with heat treatments under vacuum. For the bulk alloys, we also examined high-temperature behaviors of residual atmospheric elements and their effect on impact strength as a function of heat treatment time at 923 K. Experimental results showed that MA powder included some amount of atmospheric element that was unexpectedly difficult to remove with heat treatment. The contents of widely used argon and helium in MA powders, for example, were 130 and 5.3 mass ppm, and they were hard to remove even with treatments at 1323 K, which is considered the maximum allowable temperature. Therefore, most of these elements were introduced into bulk alloys as gas contamination. In contrast, nitrogen was effectively reduced with the treatment at 1323 K, while hydrogen could not be sufficiently removed. Residual argon and helium in bulk alloys formed bubbles at high temperatures and caused density decrease (swelling). On the other hand, hydrogen and nitrogen caused neither the formation of bubbles nor the swelling. Impact strength decreased with increased treatment time, and more remarkable decreases were observed in the alloys containing argon and hydrogen. We concluded that a proper milling atmosphere in MA for producing iron-based dispersion alloys applied to high-temperature materials was nitrogen.
Extruded and subsequently rolled sheets of AZ61 (Mg-6Al-1Zn in mass%) were tensile tested at room temperature at an initial strain rate of 1×10-3s-1. The effects of extrusion ratio and tensile direction on fracture elongation were investigated. Extrusion ratios were 3.4/100 and 1.0/100 in area reduction. Tensile direction was chosen to be 0, 45 and 90° with respect to the rolling direction. Texture change with strain was also investigated in order to understand a major dislocation slip system. We found that the magnitude of basal-plane tilt with respect to the tensile axis was a controlling factor for a major slip system and for fracture elongation. When the basal planes were tilted by more than approximately 16° from the normal direction towards the tensile direction, a major slip system was basal a dislocation slip and poor ductility was obtained. In contrast, with less tilting than 16°, a major slip system changed to non-basal a dislocation slip, which leads to better ductility. The present results indicated an importance of texture control in tensile ductility of Mg alloys.