In this paper, we present a first attempt to define the basic geometry, mechanics, and physics of the process of mechanical alloying. The geometry of the collision events which lead to particle fragmentation and coalescence is modeled on the basis of Hertzian contacts between the grinding media which entrap a certain amount of material volume between the impacting surfaces. This geometry essentially defines the volume of material affected per collision, and from this information and characteristics of the specific mill and the material being processed, impact times, powder strain rates and strains, powder temperature increase, powder cooling times, and milling times can be approximated.

The physics of mechanical alloying: A first report

It has been demonstrated that the activation of chemical reactions by mechanical energy can lead to many interesting applications, ranging from waste processing to the production of advanced materials with novel microstructures and enhanced mechanical properties. In this article, the status of three types of mechanochemical processing is reviewed—mechanical milling, mechanical alloying, and reaction milling.

The fundamentals of mechanochemical processing

The mechanical alloying process has successfully combined oxide-dispersion-strengthening with conventional gamma prime precipitation hardening for advanced gas turbine materials. INCONEL* alloy MA 6000, a mechanically alloyed Ni-base superalloy, has the highest temperature capability among commercially available superalloys. Further improvement of the intermediate temperature strength has been pursued by both increasing the gamma prime content up to 80 vol pct and controlling the additions of refractory metals. The microstructural development of these new experimental alloys is reported in this paper, especially for an alloy, nominally identified as Alloy 51, having the composition Ni-9.3 pct Cr-8.5 pct Al-6.6 pct W-3.4 pct Mo-0.15 pct Zr-0.01 pct B-l.l pct Y2O3 (wt pct). Both the primary and the secondary recrystallized microstructures of the alloy were characterized in terms of gamma grain structure, gamma prime precipitate morphology, orientation relationships, dispersoids, carbide/nitride particles, and chemical composition of intermetallic phases. The microstructural stability of the alloy under stress rupture conditions was also investigated in terms of coarsening/coalescence of gamma prime precipitates. Correlation of the microstructural information with the high temperature properties of the alloy is also briefly discussed.

Microstructural development in high volume fraction gamma prime Ni-base oxide-dispersion-strengthened superalloys

Chapter 9 – Practical applications and economic aspects of P/M superalloys

A low-pressure plasma spray (LPPS) coating of a commercial NiCoCrAlY(Ta) alloy on Inconel alloy MA 6000 was examined metallographically after 500 h of cyclic oxidation and burner rig testing for coating performance and interfacial reactions. Uncoated Inconel alloy MA 6000 was also examined for oxidation and hot corrosion resistance. Bare Inconel alloy MA 6000 has excellent oxidation resistance to 2010 °F (1100 °C) but is subject to internal sulfidation in burner rig testing at 1700 °F (925 °C) and 2000 °F (1095 °C). An LPPS coating of a NiCoCrAlY(Ta) alloy protected the Inconel alloy MA 6000 substrate from oxidation and sulfidation for 312 h at both temperatures but developed appreciable interfacial voiding after 500 h at 2000 °F (1095 °C). Spalling of the coating was observed only on burner rig test specimens run at 2000 °F (1095 °C).

High-temperature corrosion of LPPS-coated inconel alloy MA 6000

Inco has developed a very strong and corrosion re- sistant oxide dispersion strengthened superalloy, MA 6000E, by the mechanical alloying process. The alloy (15Cr–2Mo–4W–4·5Al–2·5Ti–2Ta–0·15Zr– 0·01B–1·1Y2O3–bal. Ni) exhibits a typical 100h rupture strength of 138 MN m−2 at 1093°C and 552 MN m−2 at 760°C. The oxidation and sulphidation resistances of the alloy are equal to those of IN–100 and IN–792 respectively. This paper describes how the results of laboratory research were successfully scaled-up to commercial practice. The development of a production route from mechanically alloyed powder to fully processed and heat-treated blading bar is discussed. PM/0185

G. A. J. Hack

Papers

Scale-Up Thermomechanical Processing of MA 6000E