Papers by Keyword: Casting

Abstract: Beta type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) is one of the titanium alloys which have gained much attention in dental applications. Dental precision casting is predominant for fabricating dental prostheses. However, there is a possibility for the mechanical properties of its casting to be degraded because of a α case, shrinkages and pores and a dendrite structure. One of the ways to enhance their mechanical properties is heat treatment process. Therefore, the aim of this study is to investigate the effect of aging treatment on mechanical properties and microstructure of TNTZ cast into magnesia based mold in order to improve its mechanical properties. As results, the Vickers hardness of the cast TNTZ after solution treatment is larger than that of the wrought TNTZ. The aging curve of the cast and the wrought TNTZ at an aging temperature of 673 K and 723 K exhibit almost similar pattern. For each aging time, the higher the aging temperature, the smaller the Vickers hardness for both alloys. Microstructures of cast TNTZ at various aging conditions consist of a dendritic structure and the average diameters of their grain size are around 40 μm. The diffraction peaks of precipitation of α and β phase s are detected in under aging (UA), peak aging (PA) and over aging (OA) conditions for both aging temperatures. However, the diffraction peak of ω phase is observed only in OA condition for cast TNTZ at aging temperature of 673 K. The highest tensile strength of the cast TNTZ and the wrought TNTZ at both aging temperatures are in PA condition and the elongation decrease continuously by increasing aging time. The tensile strengths of cast TNTZ in UA, PA and OA conditions at an aging temperature of 723 K are lower and their elongations are higher in comparison with those of 673 K. The high oxygen content seems to contribute to the poor elongation. SEM fractographs of the cast TNTZ at aging temperatures of 673 and 723 K in UA, PA and OA conditions show the brittle morphology with intergranular fracture that increases with increasing of aging time.

Abstract: In this research study, two light weight multi-component high entropy alloys (HEAs) consisting of six constituent elements were synthesized. The high entropy alloy having a chemical composition of Mg₃₅Al₃₃Li₁₅Zn₇Ca₅Y₅ (atomic pct.) had a density of 2.25 g/cm³, while the high entropy alloy having a composition of Mg₃₅Al₃₃Li₁₅Zn₇Ca₅Cu₅ (atomic pct.) had a density of 2.27 g/cm³. The strategy of non-equiatomic composition, high entropy of mixing coupled with low density was applied in designing the alloy systems. Disintegrated melt deposition (DMD) technique was used to synthesize the materials and characterization studies were performed on as-cast materials. The present study emphasizes on examining and understanding the microstructural development in the two light weight high entropy alloys. The formation and presence of phases and microstructural evolution were studied by interchanging yttrium and copper. Microstructural observations revealed presence of multiple phases in the developed alloys and the simplification of the microstructure when copper is used instead of yttrium. Microhardness results revealed a significant increase in hardness of of both the HEAs (3.8 – 4.2 times) when compared to AZ31 commercial magnesium alloy.Keywords: High Entropy Alloy, Magnesium, Aluminum, Casting, Microstructure

Abstract: Metal foundries use high quality sand in the casting process and produce vast amounts of used foundry sand (UFS). Thus, in order to make the best use of foundry sand in the casting process, it is essential to demonstrate an appropriate recycling method and verify the influence of regenerated foundry sand (RFS) on the mechanical properties of core. In this study, physical and chemical characterizations were conducted on the RFS and the physical properties of cores containing different proportions of RFS were investigated with respect to the flexural strength. The UFS produced in controlled conditions was recycled by a wet type method and the regular foundry sand was replaced with varying proportions of RFS by weight (0, 20, 40 and 60 wt. %). Although the gradation of RFS was analogous with the regular foundry sand, the flexural strength test indicated that the sand mixture with 20 wt. % replacement of regular foundry sand was appropriate for core making without a drastic decrease of flexural strength. The flexural strength decreased with the increase of RFS contents at replacement proportion more than 20 wt. %.

Abstract: Magnesium alloys, in which the in-situ Mg2Si particles were dispersed, were fabricated by a casting process, and the dry sliding wear behavior of the alloys was investigated. Optical microscopy revealed that the polygonal Mg2Si particles were homogeneously dispersed in the alloys. Mg2Si particle volume fractions in the alloys were 7 and 11 vol%. Although the wear loss of the alloy decreased due to the particle-dispersion, there was no difference in the wear loss between the alloys with different volume fractions. The worn surfaces of the particle-dispersed alloys were covered with the crumbled Mg2Si particles, which would prevent seizure between the alloy and the steel counterpart, leading to an improvement in the wear resistance of the alloy. The particle-dispersion slightly decreased the scatter of the coefficient of friction during the wear for the low sliding speed and load, but the effect of the dispersion was not clearly observed for the high speed and load.

Abstract: The analysis of the bending deformation effect and the central tension arising from hindered contraction of the shaped casting, its stress-strained state, leading to the formation of hot cracks in it has been given in the course of the conducted work. The influence of the main casting parameters and the mold has been studied and their relationship with emerging strains in the molded casting has been determined. The impact on the quantity of the emerging strain of bending stress under hindered contraction has been defined and confirmed by practical calculations. It has been shown that the bending stress is much higher than the emerging tensile stress in the considered conditions. It has been found that the length of the element of hindering and the compliance of a moldable mixture exerts a strong influence on the stress-strained state of the shaped casting.

Abstract: The article considers the surface roughness of compression molds castings received by casting under pressure depending on the condition of the form-building surface. The technological process of casting under pressure is presented for the "Strike plate" product, concrete technological parameters values are specified. The pilot studies of the roughness of the castings throughout the entire period of operation of a compression mold are conducted. Based on the received values the recommendations about improvement of quality of a surface of castings by drawing sheetings are submitted by phisical vapour deposition method.

Abstract: Aluminum alloys are one of the most extended groups of functional materials by reason of combination between good mechanical properties and low mass. The aim of the present paper is to test the influence of the vibrations on the AlSi10Mg (EN 1706-2010) solidification. For comparison, six lots were casted in cold and preheating molds, with or without vibrations within 50 Hz and 1050 Hz. For each casting frequency was measured the silicon phase dimension, hardness, tensile stress and impact strength. The mechanical properties increase with the vibration frequency. Increasing the vibration frequency, the structure will be refined and also the size of the silicon phase is decreasing. Considering that one source of porosity is the gas entrapped or dissolved in the liquid metal during the casting, using vibration along casting and cooling allows it’s decreasing.

Abstract: The Compacted Graphite Iron (CGI) represents an example of material with remarkable and unexplored properties, especially in terms of resistance and machinability. With better strength and stiffness than several cast irons, as Grey Iron, and better castability, machinability and thermal conductivity than others, as Ductile Irons, this alloy would be, at least theoretically, the perfect material choice for a wide range of practical applications. Nevertheless, discovered more than 50 years ago, it has failed to establish itself in a definitive way. This review intends to highlight benefits and limits in choosing CGI in casting.

Abstract: Technological developments in the field of based metal alloys have led to the implementation of novel manufacturing processes in dental practice. The aim of the study was to evaluate surface characteristics of Co–Cr dental alloys fabricated via conventional casting, computerized milling, selective laser sintering and selective laser melting. The morphology and the topography of the samples were investigated by SEM / EDAX (Model INSPECT S) and AFM (Model Nanosurf® EasyScan 2 Advanced Research). Depending on the nature and chemical composition of the samples the morphology is different. The microstructure of Co–Cr dental alloys depends on the manufacturing technique. Given to the differences in microstructural properties among the tested specimens, further differences in their technological achievement and clinical behavior can be anticipated.

Abstract: Basic information and research results of the process combined rolling-extruding have been represented, which have been used to create new energy-saving technologies for obtaining of long deformed semi-finished products of small cross-section. It has been shown that such combined processing technologies may be applicable for the machining of low ductility and low-tech aluminium alloys with high metal yield and high productivity.