Damage-tolerant Titanium Alloy Research Articles

Initiation and propagation mechanism of fatigue crack in ultra-thick titanium alloy vacuum electron beam welding joint

The investigation delved into the fatigue properties across various layers of joints in a 130-mm-thick Ti6Al4V- damage tolerance titanium alloy, which had been fabricated through vacuum electron beam welding. Microstructures in welds are inhomogeneous along the thickness direction of joints. The fatigue properties of various layers of joints exhibit minimal differences, with the fatigue limit consistently exceeding 90 % of the base metal. The cracks always initiate on the sample surface, with numerous fatigue striations present on all fractures. Additionally, many dimples are observed in all fracture zones. The fatigue crack propagation mechanism is depicted as a series connection of micro-pores. Micro-pores are formed by inward pitting of material surfaces and nucleate in local plastic deformation zones of the material. Stress concentration of microstructures is an important cause for formation of local plastic deformation zones. After high cycle fatigue experiments, martensite lath-shaped α′ phase in microstructures in the weld is broken and the broken α′ phase pins the dislocations, resulting in microscopic stress concentration.

Effect of crystal orientation on micro-stress distribution in a damage-tolerant titanium alloy TC21

Micro-stress distribution interior of TC21 alloy under abrasive processing was systematically investigated by combining EBSD data and crystal plasticity finite element model (CPFEM). The ductility enhanced of ground specimens after aging treatment, which can be attributed to the randomness of crystal orientation increased result in the decrease of micro-stress in polycrystal. For prismatic slip {101¯0}〈12¯10〉, the α-colonies with SF value of 0.16 suggest that further slip activation becomes difficult, leading to a higher local stress concentrated on grain boundaries of α-lamellae. The higher micro-stress almost distributed at the interface of α-lamellae with a preferred orientation, while in randomly oriented grains, higher micro-stress distributed interior of some grains or local interface of α-lamellae. Moreover, the maximum micro-stress in randomly oriented grains is smaller than that of preferred orientation grains.

Machinability of damage-tolerant titanium alloy in orthogonal turn-milling

The damage-tolerant titanium alloy TC21 is used extensively in important parts of advanced aircraft because of its high strength and durability. However, cutting TC21 entails problems, such as high cutting temperature, high tool tip stress, rapid tool wear, and difficulty guaranteeing processing quality. Orthogonal turn-milling can be used to solve these problems. In this study, the machinability of TC21 in orthogonal turn-milling is investigated experimentally to optimize the cutting parameters of orthogonal turn-milling and improve the machining efficiency, tool life, and machining quality of TC21. The mechanism of the effect of turn-milling parameters on tool life is discussed, the relationship between each parameter and tool life is analyzed, and the failure process of a TiAlN-coated tool in turn-milling is explored. Experiments are conducted on the integrity of the machined surface (surface roughness, metallographic structure, and work hardening) by turn-milling, and how the parameters influence such integrity is analyzed. Then, reasonable cutting parameters for TC21 in orthogonal turn-milling are recommended. This study provides strong guidance for exploring the machinability of difficult-to-cut-materials in orthogonal turn-milling and improves the applicability of orthogonal turn-milling for such materials.

Research on surface integrity in graphene nanofluid MQL milling of TC21 alloy

As a new type of damage-tolerance titanium alloy, TC21 alloy is widely used in aerospace. However, TC21 is a difficult-to-machine material owing to its low thermal conductivity, high chemical activity and low elasticity modulus. In this work, minimum quantity lubrication (MQL) with graphene nanofluid was adopted in TC21 milling. In order to evaluate the effects of graphene nanoparticle on the surface integrity, a series of milling experiments were performed under the dry, gas, pure MQL and graphene nanofluid MQL condition respectively. Results showed that the graphene additive was effective for improving the surface integrity. Overall, the results could be explained that graphene additive could enhance the cooling and lubrication performances of the oil film formed in cutting zone. The findings of this work are expected to give a feasibility and some experimental basis for the application of the graphene additive in MQL milling.

Research on surface integrity in graphene nanofluid MQL milling of TC21 alloy

As a new type of damage-tolerance titanium alloy, TC21 alloy is widely used in aerospace. However, TC21 is a difficult-to-machine material owing to its low thermal conductivity, high chemical activity and low elasticity modulus. In this work, minimum quantity lubrication (MQL) with graphene nanofluid was adopted in TC21 milling. In order to evaluate the effects of graphene nanoparticle on the surface integrity, a series of milling experiments were performed under the dry, gas, pure MQL and graphene nanofluid MQL condition respectively. Results showed that the graphene additive was effective for improving the surface integrity. Overall, the results could be explained that graphene additive could enhance the cooling and lubrication performances of the oil film formed in cutting zone. The findings of this work are expected to give a feasibility and some experimental basis for the application of the graphene additive in MQL milling.

Machinability of plunge milling for damage-tolerant titanium alloy TC21

Damage-tolerant titanium alloy, TC21, is widely used for the important components of the new-generation aircraft with high strength and durability requirements, many of which are machined by plunge milling. For optimizing the plunge milling parameters and improving machining efficiency, a number of experiments were carried out to study the machinability of plunge milling TC21. The effects of plunge milling parameters on cutting forces, the cutting temperature, and the tool life were investigated and analyzed. The process of the tool failure and the mechanism of tool wear were explored. Results showed that the cutting temperature had more influence than cutting force under the same parameters, and higher cutting heat was the main reason of the tool failure. In addition, this study showed that a large fracture of insert corner was the form of final tool failure. Furthermore, the results indicated that TiAlN-coating tool was more suitable for plunge milling TC21 than TiN-coating tool, and abrasive wear and adhesive wear were the main reasons of tool wear. Finally, reasonable parameters of plunge milling TC21 were recommended. Thus, a cutting tool with proper plunge milling parameters and tool materials should be carefully chosen to satisfy the tool life in real production.

Surface Roughness Research in Turning of Damage-Tolerant Titanium Alloy

TC21 is a first high strength and damage-tolerant titanium alloy self-developed in China, which has independent intellectual property. As it is known to all, titanium alloy TC21 is one of the most widely used materials in aerospace. The improvement of cutting quality of titanium alloy is an urgent problem. In this paper, the orthogonal experiment were carried out to study surface roughness of turning TC21. The predictive model of surface roughness in turning TC21 was built by analysis of multivariable linear regression on the basis of experiment. Statistical test results indicated the established predictive model were in highly notable test status and had high reliability. These works provide references for machining TC21.

Orthogonal Experimental Research in Milling Force of Damage-Tolerant Titanium Alloy TC21

TC21 is a first high strength and damage-tolerant titanium alloy self-developed in China, which has independent intellectual property. As it is known to all, titanium alloy TC21 is widely used in aviation and aerospace fields. The experimental study of cutting force is a important content of machining mechanism about TC21. In this paper, the orthogonal experiment were carried out to study. The predictive model of milling force in milling TC21 was built by analysis of multivariable linear regression on the basis of experiment. Statistical test results indicated the established predictive model were in highly notable test status and had high reliability.

Experiment Study of Tool Wear and Surface Integrity in High Speed Milling of a New Damage-Tolerant Titanium Alloy

TC4-DT is a new damage-tolerant titanium alloy. In the paper, a series of experiments on tool wear and surface integrity in high speed milling of the alloy were carried out. The tool lives of different tool materials were studied and the wear mechanism of cutting tools was also investigated. Then surface integrity, including surface roughness, microhardness and metallurgical structure was studied and analyzed in high speed milling at different tool wear status. Results showed that K10 is the most suitable cutting tool after considering a combination of factors. And good surface integrity could be obtained in high speed milling of TC4-DT under all cutting situations. In addition, even with acutely worn stages, there has been no so-called serious hardening layer (or white layer) according to the study of microhardness and metallurgical structure beneath the machined surface.

Experimental study in high speed milling of titanium alloy TC21

In this paper, a number of experiments were carried out to study the machinability of a new damage-tolerant titanium alloy (TC21). Firstly, the effects of milling parameters, tool material, and tool wear on cutting forces were investigated. Secondly, the effects of milling parameters and tool wear on cutting temperature were studied. Finally, the effect of tool material on tool life was explored. Results showed that cutting force, cutting temperature, and tool life were greatly influenced by milling parameters, tool material, and tool wear. Thus, cutting tool matching with proper milling parameters should be carefully chosen to satisfying the tool life in actual production.

Experimental Study in HSM of Titanium Alloy TC4-DT

In this paper, a series of experiments were carried out on normal and high speed milling of a new damage-tolerant titanium alloy. The effects of milling parameters on cutting force and cutting temperature were investigated. The tool life of three commonly used cutters, such as WK10, WMG40 and WXN15, were studied. Result shows that the tool life of cutter WXN15 was the longest one when using the same flank wear VB as a standard, and cutter WK10 had a longer too life than cutter WMG40. Thus cutter WXN15 was the most suitable cutting tool to machining TC4-DT, and cutter WK10 was better than cutter WMG40.

Research on High Strength and High Toughness Titanium Alloy with Damage Tolerance

As the concept of aerospace design is changed, research objectives of titanium alloys also changed from high strength to high damage tolerance. High strength, high toughness titanium alloys with damage-tolerance have been investigated under the support of a national project since 2003. TC21 titanium alloy is the first Chinese-developed high strength, high toughness and damage-tolerance titanium alloy. The mechanical property of TC21 alloy is sensitive to solution temperature and aging temperature. The rods of TC21 alloy with the diameter of 20mm and 90mm possess good mechanical properties after solution at 900°C followed by aging at 600°C.