Materials Science Forum Vols. 618-619

Abstract: Direct manufacturing of metallic materials has gained widespread interest in the past decade. Of the methods that are currently under evaluation, wire-fed electron beam deposition holds the most promise for producing large-scale titanium parts for aerospace applications [1]. This method provides the cleanest processing environment as the deposition is performed under vacuum. While this environment is beneficial in preventing contamination of the deposit, there is the potential for preferential vaporization of high vapor pressure elements during the deposition process. This can lead to detrimental chemistry variations, which can have negative impacts on physical and mechanical properties. Past experience has shown that deposition of the alloy Ti-6Al-4V using electron beam direct manufacturing can produce material with aluminum content below the specification minimum [2]. As aluminum has a high vapor pressure with respect to titanium and vanadium, it preferentially vaporizes from the molten pool. This aluminum loss scales with the size of the molten pool and thus the chemical content can vary throughout the build. Compensating for this loss is necessary in order to achieve nominal chemistry in the deposited material. This paper examines established processing conditions for direct manufacturing of titanium, quantitatively determines deposited alloy chemistry changes under various conditions, and suggests a feedstock composition that will result in deposited material with nominal Ti-6Al-4V chemistry.

Abstract: Removal rates for machining titanium alloys are an order of magnitude slower than those for aluminum. The high strength and hardness coupled with the relatively low elastic modulus and poor thermal conductivity of titanium contribute to the slow speeds and feeds that are required to machine titanium with acceptable tool life. Titanium has extremely attractive properties for air vehicles ranging from excellent corrosion resistance to good compatibility with graphite reinforced composites and very good damage tolerance characteristics. At current Buy to Fly ratios, the F-35 Program will consume as much as seven million pounds of titanium a year at rate production. This figure is nearly double that of the F-22 Program, which has a much higher titanium content. As much as 50% of the final cost of titanium parts can be attributed to machining. Specifically, in this task, we are working to improve the material removal rate of titanium to reduce cost. Lockheed Martin is evaluating the potential to use lasers to heat the material ahead of the tool to reduce its strength. Coupled with other technologies that can improve the tool life and prevent the titanium material from welding to the tool, there is hope for a practical solution using similar milling machines to those which exist today, if not a simple retro-fit option. This presentation will present the current progress of this project and its potential impact to the Joint Strike Fighter.

Abstract: Titanium has extremely attractive properties for air vehicles ranging from excellent corrosion resistance to good compatibility with graphite reinforced composites and very good damage tolerance characteristics. At current Buy to Fly ratios, the F-35 Program will consume as much as seven million pounds of titanium a year at rate production. This figure is nearly double that of the F-22 Program, which has a much higher titanium content. Lockheed Martin has initiated “Project Black Ti” to reduce the cost of titanium parts by reducing the titanium consumption but not the quantity of titanium parts. Ultimately, we want to reduce the inherent waste in the current processing of titanium alloy products. The Kroll process, by which most titanium product is made today, is nearly 60 years old. Kroll himself predicted the process would be replaced within 15 years due to inherent inefficiencies – in 1950. Titanium is also mis-characterized as a precious metal, which it is not. It is the ninth most abundant element on the earth’s surface. Aluminum by comparison is the third most abundant but has a much more efficient method to convert it to a usable form. Until the turn of the 20th century, aluminum was considered to be as precious as platinum until the Bayer Process brought prices down from $1200/kg to $0.60/kg. Regarding titanium, one way to improve efficiency and buy less material to make the same parts is via Powder Metallurgy (PM). Until recently, titanium alloy powder was very expensive. However, new methods of producing titanium alloy have been developed which generate powder as an output versus massive ingots, which require multiple melts to achieve homogeneity. With powder, in theory, we should be able to get much closer to net shape and reduce the initial buy and reduce significant machining costs. These low cost titanium powders are becoming commercially available, which has the potential to initiate a paradigm shift in the applications of titanium. PM technologies and the consolidation of these new powders are now economically viable with the potential cost of the new powders running approximately an order of magnitude less than conventional PM grade powders. This paper will present the current status of “Project Black Ti” and its potential impact to the F-35 program.

Abstract: The effect of Aluminum equivalent and Molybdenum equivalent on the strength and fracture toughness of titanium alloys was studied in this paper. The result shows that the tensile strength of the alloy increases with increasing of aluminum equivalent and molybdenum equivalent and the fracture toughness decreases gradually, the effect of aluminum equivalent is comparatively more conspicuous. A suitable value range of aluminum equivalent and molybdenum equivalent of high strength and high toughness titanium alloys are obtained from the analysis, based on this, a new type of high strength and high toughness titanium alloy BTi-6554 (Ti-4Al-5Mo-5V-6Cr) was developed, which has good combination of strength and fracture toughness and has the characteristics of high strength and high toughness.

Abstract: This paper is concert about the mechanical property of high strength and high toughness titanium alloy BTi-6554 (Ti-6Cr-5Mo-5V-4Al) bars. The results show that: in β-phase zone solid solution + aging treatment condition, the strength and fracture toughness of the alloy at room temperature can reach a higher level while inα+β)-phase solution + aging treatment condition, the plastic property is relatively high. Compared with Ti-1023 and VT22 alloy bars produced by the similar processing procedure, the alloy shows improved properties combined in strength and toughness. BTi-6554 is a new type of titanium alloy with high structural efficiency, and has a good prospect for commercial and application.

Abstract: The effects of solution and aging treatment on the mechanical properties of BTi-6554 alloy titanium were investigated. The results showed: As to βsolution and aging treatment, the increase of fracture toughness is quite conspicuous as the solution temperature was raised, but the change of strength and plasticity is not obvious; As to (α+β) solution and aging treatment, the decline of fracture toughness and plasticity is quite conspicuous as the solution temperature increased, but the strength increased. The strength of (α+β) solution and aging treatment is higher than that of βsolution and aging treatment, but the fracture toughness is relatively lower. As the aging temperature increased, the strength of the alloy gradually decreased, but the plasticity and fracture toughness gradually improved and the improvement of fracture toughness is quite conspicuous. A better combination of strength-toughness-ductibility could be obtained under the heat treatment as solution at 900~930 oC and aging treatment at 560~590 oC.

Abstract: When trying to calculate the approximate constitution of as-cast tin containing aluminium alloys one has to cope with a combination of intricacies: (i) Scheil solidification simulation may reflect strong enrichment of alloying components, especially in multicomponent alloys, thus leaving the safe ground of the underlying thermodynamic database. (ii) Liquid demixing often intensifies by addition of many components to Al-Sn alloys, thus forming monotectic reactions, boosting the segregation and aggravating the first effect. (iii) Scheil simulation in multicomponent Al-x-y-z-Sn alloys not only combines the first two problems, moreover, the current versions of major thermodynamic software packages are not able to perform the Scheil simulation if liquid demixing and monotectic reactions occur. These intricacies are worked out and the development of a dedicated Al-Si-Cu-Mg-Sn thermodynamic database for large composition ranges is presented. Calculations are compared to experimental data of an Al-7.5Si-3.5Cu-0.3Mg-0.1Sn alloy and the need for specific follow-up work is identified.

Abstract: Compared with the actual operation, computational simulation will save the cost and provide more valuable references or guiding significance for the real production. Using professional forming software DEFORM-3D, the upsetting process of WE43 magnesium alloy was simulated. Based on the actual flow stress data, the simulation model of WE43 magnesium alloy was created in DEFORM-3D. Results show that the uniform distribution of the temperature of WE43 magnesium alloy during the forming process is beneficial to the structural homogeneity and contributes to excellent flowing property. There is the stress concentration in the edge and slide face of the billet. So during the process of compression, the fracture will appear earlier in the edge and slide face of the sample.

Abstract: A brief overview of the role of computational materials science and engineering in the ARC Centre of Excellence for Design in Light Metals is presented. A recent example of designing precipitate structures in Al alloys for simultaneous increases in strength and elongation is used to highlight the spirit of the approach.

Abstract: Aluminum casting is widely used in aeronautical, automobile and other industries nowadays. The Cellular Automaton (CA) method was modified to simulate the microstructure evolution of Al alloy casting. Simulated program code was developed and applied into Al casting production. A nucleation model was investigated based upon the experimental data. The solute diffusion in the liquid and solid phases was also considered in developing a grain growth model. With the developed models, not only grain structure but also dendritic microstructure can be predicted during the solidification process. The microstructure simulation of the Al alloy turbine wheel was studied in detail.