The impact behavior of molten metal on the mold shell in gravity casting of large titanium alloy castings by investment precision castings was studied.The physical and mechanical models of the impact of molten metal o...The impact behavior of molten metal on the mold shell in gravity casting of large titanium alloy castings by investment precision castings was studied.The physical and mechanical models of the impact of molten metal on the mold shell during the pouring process were constructed using numerical simulation.The effects of molten metal pouring rate and pouring weight on the maximum impact force of the mold shell were studied.The research results indicated that during the entire pouring process,the impact force of the first molten metal contacting the mold shell was higher than subsequent molten metal.The maximum impact force increased with the increase of pouring rate and pouring weight.The total impact force of the molten metal on the mold shell was composed of the instantaneous impact force converted from instantaneous impulse and itself gravity.The instantaneous impact force of the molten metal that first impacts the mold shell was much greater than its own gravity,while the impact force of the molten metal at the end of pouring was much less than its own gravity.The maximum impact force on the mold shell of a large casting with a pouring weight of 800kg was about three times higher than that of a medium-sized casting with a pouring weight of 80kg.The difference in the total impact force on the mold shell between them mainly comes from the instantaneous impact force converted from instantaneous impulse.展开更多
The aim of this paper was to study the reaction between a Ti-6Al-4V alloy and boron nitride based investment shell molds used for investment casting titanium. In BN based investment shell molds, the face coatings are ...The aim of this paper was to study the reaction between a Ti-6Al-4V alloy and boron nitride based investment shell molds used for investment casting titanium. In BN based investment shell molds, the face coatings are made of pretreated hexagonal boron nitride （hBN） with a few yttria （Y2O3） and colloidal yttria as binder. The Ti-6Al-4V alloy was melted in a controlled atmosphere induction furnace with a segment water-cooled copper crucible. The cross-section of reaction interface between Ti alloys and shell mold was investigated by electron probe micro-analyzer （EPMA） and microhardness tester. The results show that the reaction is not serious, the thickness of the reacting layer is about 30-50 μm, and the thickness of α-case is about 180-200 pro. Moreover the α-case formation mechanism was also discussed.展开更多
At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce ma...At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce manufacturing costs and explore new markets for the process. Currently, the main problems for investment casting of TiAl alloys are cracks, porosities, and surface defects. To solve these problems, many studies have been conducted around the world, and it is found that casting defects can be reduced by improving composition and properties of the shell molds. It is important to make a summary for the related research progress for quality improvement of TiAl castings. So, the development on refractory composition of shell molds for TiAl alloy investment castings was reviewed, and research progress on deformability of shell mold for TiAl alloy castings both at home and abroad in recent years was introduced. The existing methods for deformability characterization and methods for improving the deformability of shell molds were summarized and discussed. The updated advancement in numerical simulation of TiAl alloy investment casting was presented, showing the necessity for considering the deformability of shell mold during simulation. Finally, possible research points for future studies on deformability of shell mold for TiAl alloy investment casting were proposed.展开更多
Research and development of cast superalloys and processing for turbine blades in BIAM during the last 35 years have been reviewed briefly in this paper.
The meniscus shell plays an important role in slab quality and process operation for continuously cast steel. One decisive reason is initial solidifying shell and growing dendrite under the mechanical stress caused by...The meniscus shell plays an important role in slab quality and process operation for continuously cast steel. One decisive reason is initial solidifying shell and growing dendrite under the mechanical stress caused by mold oscil- lation and liquid steel flow to generate disturbance of casting. The mechanical state of meniscus shell was analyzed using mathematical models in combination with thermo-physical properties and flow rate of steel to shed light on the formation of initial defects. The results show that the mold oscillation is a critical factor on the initial crack formation because the periodic stress makes the shell bending. The formed crack may also expand and propagate due to the fol- lowing secondary cooling and straightening behavior. The primary dendrite has high possibility to be broken by fluid flow in the solidification front to lead to the non-uniform thickness of solidifying shell. The inter-dendrite bridging is also likely to be formed to produce other internal defects, such as air hole and solute enrichment in the residual mol- ten steel located in the bridging area.展开更多
文摘The impact behavior of molten metal on the mold shell in gravity casting of large titanium alloy castings by investment precision castings was studied.The physical and mechanical models of the impact of molten metal on the mold shell during the pouring process were constructed using numerical simulation.The effects of molten metal pouring rate and pouring weight on the maximum impact force of the mold shell were studied.The research results indicated that during the entire pouring process,the impact force of the first molten metal contacting the mold shell was higher than subsequent molten metal.The maximum impact force increased with the increase of pouring rate and pouring weight.The total impact force of the molten metal on the mold shell was composed of the instantaneous impact force converted from instantaneous impulse and itself gravity.The instantaneous impact force of the molten metal that first impacts the mold shell was much greater than its own gravity,while the impact force of the molten metal at the end of pouring was much less than its own gravity.The maximum impact force on the mold shell of a large casting with a pouring weight of 800kg was about three times higher than that of a medium-sized casting with a pouring weight of 80kg.The difference in the total impact force on the mold shell between them mainly comes from the instantaneous impact force converted from instantaneous impulse.
文摘The aim of this paper was to study the reaction between a Ti-6Al-4V alloy and boron nitride based investment shell molds used for investment casting titanium. In BN based investment shell molds, the face coatings are made of pretreated hexagonal boron nitride （hBN） with a few yttria （Y2O3） and colloidal yttria as binder. The Ti-6Al-4V alloy was melted in a controlled atmosphere induction furnace with a segment water-cooled copper crucible. The cross-section of reaction interface between Ti alloys and shell mold was investigated by electron probe micro-analyzer （EPMA） and microhardness tester. The results show that the reaction is not serious, the thickness of the reacting layer is about 30-50 μm, and the thickness of α-case is about 180-200 pro. Moreover the α-case formation mechanism was also discussed.
基金financially supported by the Technical Development Foundation of China Academy of Machinery Science and Technology under project:Investment Casting Technology Research for TiAl Alloy Turbocharger Turbine
文摘At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce manufacturing costs and explore new markets for the process. Currently, the main problems for investment casting of TiAl alloys are cracks, porosities, and surface defects. To solve these problems, many studies have been conducted around the world, and it is found that casting defects can be reduced by improving composition and properties of the shell molds. It is important to make a summary for the related research progress for quality improvement of TiAl castings. So, the development on refractory composition of shell molds for TiAl alloy investment castings was reviewed, and research progress on deformability of shell mold for TiAl alloy castings both at home and abroad in recent years was introduced. The existing methods for deformability characterization and methods for improving the deformability of shell molds were summarized and discussed. The updated advancement in numerical simulation of TiAl alloy investment casting was presented, showing the necessity for considering the deformability of shell mold during simulation. Finally, possible research points for future studies on deformability of shell mold for TiAl alloy investment casting were proposed.
文摘Research and development of cast superalloys and processing for turbine blades in BIAM during the last 35 years have been reviewed briefly in this paper.
基金Item Sponsored by National Natural Science Foundation of China(51004031)Fundamental Research Funds for the Central Universities of China(N140205002)National Outstanding Young Scientist Foundation of China(50925415)
文摘The meniscus shell plays an important role in slab quality and process operation for continuously cast steel. One decisive reason is initial solidifying shell and growing dendrite under the mechanical stress caused by mold oscil- lation and liquid steel flow to generate disturbance of casting. The mechanical state of meniscus shell was analyzed using mathematical models in combination with thermo-physical properties and flow rate of steel to shed light on the formation of initial defects. The results show that the mold oscillation is a critical factor on the initial crack formation because the periodic stress makes the shell bending. The formed crack may also expand and propagate due to the fol- lowing secondary cooling and straightening behavior. The primary dendrite has high possibility to be broken by fluid flow in the solidification front to lead to the non-uniform thickness of solidifying shell. The inter-dendrite bridging is also likely to be formed to produce other internal defects, such as air hole and solute enrichment in the residual mol- ten steel located in the bridging area.
