July/August_AMP_Digital

6 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 | J U L Y / A U G U S T 2 0 1 8 Having been deeply involved in the titanium industry during the “his- toric” times, I was anxious to read “Titanium: A Historic and Current Per- spective” [February/March and April issues]. I’m sorry to say that it left me wondering why so much important in- formation about process developments and applications were ignored. Much effort seemed to dwell on newer tech- nology to produce lower cost raw ti- tanium and powder process develop- ments for making closer to net shapes. PM [powder metallurgy] part manufac- ture has been around for several de- cades and I’m sure there is a continu- ing push to improve efficiency. It is not a new concept. However, conspicuous by its absence was the mention of cast- ings when discussing near net shapes. The word casting is never mentioned in the article. Development of lost wax invest- ment, sand, and semi-permanent mold titanium casting technology occurred during this historic time in the 1960s through 1980s without comment. Like- wise, during that same period, many im- portant applications of such products were ignored. Some of these include in- vestment cast aircraft engine frames, tiny switch guards used in the cockpit of the Space Shuttle, robust sand cast bracketry that attached the Space Shut- tle to the rocket engine and external fuel tanks, aircraft brake torque tubes for the B-1 bomber and others, hot gas nozzles that allow the Harrier Jump Jet to take off vertically, thousands of mis- sile wings, and many other significant applications of cast parts. Then there are the non-aerospace applications that were ignored. Pumps and valves are obvious casting applica- tions but are never mentioned. There are also waterjet hydrofoil propulsion impellers made of cast titanium, nucle- ar submarine valve balls, and desalina- tion compressor impellers. The article mentions a wide variety of nonmilitary/ aerospace applications including den- tal, marine, chemical processing, and eyeglass frames but doesn’t say how they were made. Even the cast titanium golf club heads so common today came into being almost 30 years ago. With regard to specifications, I wonder why AMS 4928 was ignored in the tabulation. During my years in the industry, it was probably themost wide- ly called out wrought spec. Speaking of specs, it seems that the casting industry was again ignored. There happens to be Mil-T, ASTM, as well as AMS specs specif- ically for cast titanium hardware some going back several decades, yet there is no mention in the table of specs. Bottom line, while I was pleased to see ongoing development to lower ma- terial costs, there is more than just the powdermetallurgyapproach tonear net shape manufacturing that can benefit. Jeremy Newman ASM Life Member TITANIUM SERIES IGNORES CASTING TECHNOLOGY FEEDBACK We welcome all comments and sugges- tions. Send letters to frances.richards@ asminternational.org. AUTHORS’ RESPONSE We would like to thank Mr. New- man for his informative response to our articles on titanium science, tech- nology, and applications. He has clear- ly made the case for titanium castings, whichwedidnot discuss. Inanoverview article, we strive to hit the high points, and cast and wrought products are a much larger segment of the total titani- um market. Castings provide a cost ef- fective alternative to cast and wrought products, with tensile properties at the same levels but with some degradation in ductility of the cast parts. However, S-N fatigue is inferior to the cast and wrought material (and powder metal- lurgy parts) as shown in the diagram on this page, negating use in critical applications. We justify our discussions of the powder metallurgy approach, particu- larly the additive manufacturing tech- nique. We believe this is the fabrication approach of the future as it provides mechanical properties generally at or above cast and wrought levels and is cost effective with a greatly reduced buy-to-fly ratio. Francis H. (Sam) Froes and Ashraf Imam