1412 Nickelaluminumbronze

Nickel-aluminum-bronzes (NAB) are complex alloys consisting of Ni, Al, Fe, and Mn as major alloying elements. Cast NAB is used for propeller blades and hubs, valve bodies, and other components exposed to seawater. NAB alloys, as a class, have excellent corrosion and cavitation resistance in combination with relatively high strength and ductility. NAB alloys are used in both a cast and wrought form.

The microstructural development and resulting mechanical and environmental properties of cast NAB alloys are dependent on alloy chemistry and thermal history. In large castings local variation in chemistry may be outside the bulk chemical limits imposed by specification. In addition, local differences in cooling rates (large castings may take more than a week to cool) also affect the type, volume fraction, and morphological characteristics of matrix and precipitating phases.

One of the most widely used NAB alloys is UNS C95800, which has a nominal composition of Cu-9Al-5Ni-5Fe-1Mn. Laser-based rapid manufacturing was performed using the Penn State process and compared to conventionally cast NAB. Laser deposition was conducted under both argon and nitrogen atmospheres and no practical differences in chemistry or tensile properties were noted. Table 14.7 lists the results of tensile testing.

Table 14.8 shows the chemical analysis of the powder and laser-deposited material used for the mechanical testing shown above. Note that there is essentially no difference between the starting powder and the laser deposits using either argon or nitrogen as the inert cover gas. Obviously, nitrogen would be preferred since the cost of nitrogen is about five times lower than that of argon.

Microstructural analysis of laser deposits has also been made using powder feedstock with a slightly lower aluminum content and is shown in Table 14.9. The microstructures in Figs. 14.8- 14.10 show that the laser-deposited microstructure is much finer and more homogenous than a conventional casting. The laser-formed microstructure consists of a network of proeutectoid a surrounding prior P dispersed with various k phases.

624 ADVANCES IN RAPID PROTOTYPING AND MANUFACTURING TABLE 14.7 Mechanical Properties of Nickel-Aluminum-Bronze

Test UTS YS

Process Source Condition Direction (MPa) (MPa) % Elong. % R of A

Test UTS YS

Process Source Condition Direction (MPa) (MPa) % Elong. % R of A

Penn State

ARL-Penn

As deposited

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