April_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 0 2 3 durability as high-strength titanium al- loy parts, but at a much reduced cost. It should be noted that among the four previously mentioned processes, only the PM HIP process results in compo- nents with a unique homogenous mi- crostructure observable at any of their cross sections. Near net shape components made by AM from the powder of high-strength titanium alloys have a buy-to-fly ra- tio that is comparable to the PM HIP process. However, the high cost of ti- tanium powder required for AM, high energy consumption, and issues with low, medium, and high temperatures (secondary hardening) that depend on the required properties. Formation of near net shapes by PM HIP allows manufacturing various types of complex-shaped aircraft com- ponents [2] . The process enables precise geometry of complex shapes, blanks up to 55 inches in diameter, and properties close to forgings. The cost of critical components made by PM HIP is generally higher than the cost of the same components made by HW. However, small batches of large-section complex-shape articles are economically feasible to produce by PM HIP rather than HW, especially for NNS products. NNS critical components made by PM HIP are cost-effective due to minimal waste. They also have a sig- nificantly lower buy-to-fly ratio than HW components. Figure 1 shows an example NNS part made by PM HIP from Ti-6Al-4V al- loy powder (impeller for gas compressor working in a corrosive environment). However, the high cost of titanium powder, its affinity to oxidation, and is- sues with machining limit the applica- tion of critical components made by PM HIP from powder. Critical components made by PM HIP using HSCR steel powder are a lower-cost alternative to components made with titanium alloy powder using the same process. The HSCR steel com- ponents offer the same lifetime and machining limit the practicality of us- ing AM to make components from high- strength titanium alloys. The lowest cost process for mak- ing critical components out of the four processes described above involves casting + HIP, including precision in- vestment casting and vacuum casting, followed by HIP, finish machining, and surface quality improvement (if neces- sary) and hardening. The combination of casting and HIP results in slightly less strength compared to the HW process. The combination of vacuum investment casting and HIP is a feasible option for Fig. 1 — Impeller for gas compressor made by PM HIP from Ti-6Al-4V alloy powder. Courtesy of LNT PM Inc. TABLE 1 – MECHANICAL PROPERTIES OF HSCR STEEL AND Ti-6Al-4V ALLOY Processes HW + Hardening PM HIP+ Hardening SLM + Annealing Casting + HIP Materials HSCR Ti-6-4 HSCR Ti-6-4 HSCR Ti-6-4 HSCR Ti-6-4 Density (ρ), lb/in 3 0.280 0.160 0.280 0.160 0.280 0.160 0.280 0.160 Modulus Elasticity (E), ksi 30100 16670 28900 16000 29800 16500 28200 15000 Specific Stiffness (E/ρ) 107500 104160 103210 100000 106430 103130 100700 93750 Tensile Strength (UTS), ksi 294 165 290 159 291 162 275 140 Specific Strength (UTS/ρ) 1050 1030 1037 994 1039 1013 980 875 Yield Strength (YS), ksi 226 151 220 145 223 148 210 125 Fatigue Limits (S) at 10 7 Cycles, ksi 120 100 116 90 117 90 90 - Elongation (El), % 10 10 10 9 10 10 8-10 5-10 Reduction of Area (RA), % 36 34 40 30 34 30 32-34 - Fracture Toughness (K 1C ), ksi√in 65 70 65 75 60 65 60 - Charpy V-Notch Impact Toughness Energy (CVN), ft-lb 22 16 20 14 16 14 15 -