https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1037&context=mepubs

Additive manufacturing of Ti6Al4V alloy: A review

An overview of the machinability of aeroengine alloys

Significant advances have been made in understanding the behaviour of engineering materials when machining at higher cutting conditions from practical and theoretical standpoints. This approach has enabled the aerospace industry to cope with constant introduction of new materials that allow the engine temperature to increase at a rate of 10 °C per annum since the 1950s. Improvements achieved from research and development activities in this area have particularly enhanced the machining of difficult-to-cut nickel base and titanium alloys that have traditionally exhibited low machinability due to their peculiar characteristics such as poor thermal conductivity, high strength at elevated temperature, resistance to wear and chemical degradation, etc. A good understanding of the cutting tool materials, cutting conditions, processing time and functionality of the machined component will lead to efficient and economic machining of nickel and titanium base superalloys. This paper presents an overview of major advances in machining techniques that have resulted to step increase in productivity, hence lower manufacturing cost, without adverse effect on the surface finish, surface integrity, circularity and hardness variation of the machined component.

Key improvements in the machining of difficult-to-cut aerospace superalloys

Additive Manufacturing of titanium components holds promise to deliver benefits such as reduced cost, weight and carbon emissions during both manufacture and use. To capitalize on these benefits, it must be shown that the mechanical performance of parts produced by Additive Manufacturing can meet design requirements that are typically based on wrought material performance properties. Of particular concern for safety critical structures are the fatigue properties of parts produced by Additive Manufacturing. This research evaluates the fatigue properties of Ti–6Al–4V specimens produced by the Selective Laser Melting additive manufacturing process. It was found that the fatigue life is significantly lower compared to wrought material. This reduction in fatigue performance was attributed to a variety of issues, such as microstructure, porosity, surface finish and residual stress. There was also found to be a high degree of anisotropy in the fatigue performance associated with the specimen build orientation.

Fatigue performance evaluation of selective laser melted Ti–6Al–4V

Chip formation during dry turning of Ti6Al4V alloy has been examined in association with dynamic cutting force measurements under different cutting speeds, feed rates and depths of cut. Both continuous and segmented chip formation processes were observed in one cut under conditions of low cutting speed and large feed rate. The slipping angle in the segmented chip was 55°, which was higher than that in the continuous chip (38°). A cyclic force was produced during the formation of segmented chips and the force frequency was the same as the chip segmentation frequency. The peak of the cyclic force when producing segmented chips was 1.18 times that producing the continuous chip. The undeformed surface length in the segmented chip was found to increase linearly with the feed rate but was independent of cutting speed and depth of cut. The cyclic force frequency increased linearly with cutting speed and decreased inversely with feed rate. The cutting force increased with the feed rate and depth of cut at constant cutting speed due to the large volume of material being removed. The increase in cutting force with increasing cutting speed from 10 to 16 and 57 to 75 m/min was attributed to the strain rate hardening at low and high strain rates, respectively. The decrease in cutting force with increasing cutting speed outside these speed ranges was due to the thermal softening of the material. The amplitude variation of the high-frequency cyclic force associated with the segmented chip formation increased with increasing depth of cut and feed rate, and decreased with increasing cutting speed from 57 m/min except at the cutting speeds where harmonic vibration of the machine occurs.

Characteristics of cutting forces and chip formation in machining of titanium alloys

Titanium and titanium alloys are excellent candidates for aerospace applications owing to their high strength to weight ratio and excellent corrosion resistance. Titanium usage is, however, strongly limited by its higher cost relative to competing materials, primarily aluminum alloys and steels. Hence the advantages of using titanium must be balanced against this added cost. The titanium alloys used for aerospace applications, some of the characteristics of these alloys, the rationale for utilizing them, and some specific applications of different types of actual usage, and constraints, are discussed as an expansion of previous reviews of β alloy applications. [1,2]

An overview on the use of titanium in the aerospace industry

This study has examined the potential for enhancing the fatigue performance of Ti–15V–3Cr–3Al–3Sn sheet through variations in heat treatment and thermomechanical processing procedures. Processing variants included conventional solution treatment and aging, solution treatment with duplex- and triplex-ages, and cold and warm rolling followed by aging. Tensile and smooth fatigue performance of each processing route were evaluated and compared to ‘standard’ commercial practice. These processing avenues provided a wide range of microstructures with tensile strengths ranging from 1070 to 1610 MPa. Enhancements in fatigue performance were dependent on processing and stress level. At high stresses, i.e. within the low cycle regime, a 15% improvement in the maximum stress for a fixed 30 000 cycle lifetime was achieved. At lower stresses, i.e. within the high cycle fatigue ‘limit’ regime, a 50% improvement relative to the standard heat treatment was achieved. A good correlation of fatigue and tensile strengths was observed; generally, the smooth fatigue properties improved as the tensile strength increased.

R.R. Boyer

Papers

An overview on the use of titanium in the aerospace industry

The influence of thermomechanical processing on the smooth fatigue properties of Ti–15V–3Cr–3Al–3Sn