Chemical high-temperature alloys

Depth-of-Gut Notching. Depth-of-cut notching (DOCN) is a localized wear process common when machining materials such as austenitic stainless steels or high temperature alloys. Notching is attributed to the chemical reaction of the tool material and the atmosphere, or to abrasion by the hard, sawtooth outer edge of the chip. DOCN may lead to tool fracture. 

A durable protective coating for high-temperature alloys can be achieved by CVD. Normally, we must consider alloy stabilization in addition to chemical reaction in a controlled environment. The results define the nature of coatings for high-temperature corrosion protection, namely, a thin (1-2 pm) diffused silicon layer that covers the surface and penetrates even the smallest defects, cracks, etc., on the alloy to be protected. This surface modification treatment by CVD can be adapted to other alloys and is technologically simple and relatively inexpensive. 

The screening logic for selecting secondary salt coolants requires that the elements constituting the coolant must form compounds that (1) have chemical stability at the required temperatures, (2) melt at useful temperamres and are not volatile, and (3) are compatible with high-temperature alloys, graphite, and ceramics. 

Nickel and Nickel Alloys A wide range of ferrous and nonfer-rous nickel and nickel-bearing alloys are available. They are usually selected because of their improved resistance to chemical attack or their superior resistance to the effects of high temperature. In general terms their cost and corrosion resistance are somewhat a func tion of their nickel content. The 300 Series stainless steels are the most generally used. Some other frequently used alloys are hsted in Table 10-35 together with their nominal compositions. For metallurgical and corrosion resistance data, see Sec. 28. 

Corrosion Resistance Possibly of greater importance than physical and mechanical properties is the ability of an alloy s chemical composition to resist the corrosive action of various hot environments. The forms of high-temperature corrosion which have received the greatest attention are oxidation and scaling. 

For research of alloys in the liquid state the chemical analysis can be applied only then, when high-temperature samples sharply to chill, that is to temper. But it can cause changes in the state of the system. That is why it is the best to determine composition of alloys in the liquid state. 

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