Showing 2 results for Intermetallic Compounds.
S. M. Miresmaeili and S. Shabestari,
Volume 25, Issue 1 (7-2006)
Abstract
The formation of microporosity in modified Al-Si alloys has been reviewed in the present study. A major concern in modification is the increased tendency to form microporosity in the macro-shrinkage free Al-Si alloy castings. It has also been demonstrated that at low hydrogen contents (0.1cc/ 100g, Al), where only shrinkage porosity should occur, the effect of Sr-modification on porosity content is not considerable, indicating that the increase in porosity is due to an increase in gas porosity. Modification treatment, however, does not add hydrogen to the melt, nor does it increase the rate of regassing of the liquid, revealing that it can not enhance pore formation by increasing the melt hydrogen content. Modification treatment raises the freezing range (4-10 oC), but this increased freezing range exerts only a very small effect on microporosity formation, which cannot, by itself, explain the increased tendency to microporosity formation observed in modified alloys. The presence of modifiers slightly decreases the surface tension of the melt (5%), although this decrease in surface tension is not sufficiently high to considerably enhance pore formation in modified alloys. Many researchers have reported that modification treatment might favour the formation of porosity due to its effect on oxide use in the heterogeneous pore formation although the systematic observation of pores has shown that SrO does not take part in pore fomation in Sr-modified alloys. Strontium and other modifiers which increase pore formation (Na and Ca) in Al-Si alloys have a high chemical affinity to form complex intermetallic compounds with Si and Al. Systematic observation of pores have shown that Sr-rich intermetallics take part in pore formation. Thus, Sr-modification may increase the porosity content through the formation of Sr-rich compounds during solidification.
S. Arjmand, G. H. Akbari, G. R. Khayati,
Volume 39, Issue 4 (2-2021)
Abstract
The purpose of the present work is to investigate the influence of the number of weld-passes on microstructure, hardness and residual stresses of composite coatings composed of Ti-Al-Si intermetallic compounds. In this regard, surface coating of pure Ti was carried out using one and two passes of tungsten inert gas (TIG) welding with an Al filler alloy (grade 4043). Phase and structural evaluations of the coatings were investigated by X-ray diffraction, optical and scanning electron microscopies. microhardness and residual stress values of the coatings were measured using ASTM E384-HV device and the Sin2ψ method, respectively. The results showed that as the number of welding passes increased or the dilution ratio decreased, the volume fraction of Ti5Si3-Al3Ti intermetallic phases within the fusion zone increased and the volume fraction of martensite phase in the heat affected zone decreased. As a result, the average hardness value of the coating increased to be about 130 % compared to that of the pure Ti substrate. The tensile residual stresses at the center line of fusion zone were 165 ± 30 and 210 ± 35 MPa for the coatings prepared in one and two welding passes, respectively.
