For elevated temperatures, other materials, Mechanical Engineering

For Elevated Temperatures, Other Materials

 High temperature creep is a significant phenomenon to be guarded in various machines like gas turbines, missiles, reentry vehicles and propulsion engines. Ferritic and another stainless steel are good against creep but merely to limited extent. Refractory metals and their alloys are beneath close investigation for this point. The goal is not still achieved and some developments are still proprietary. This will be worthwhile to note several developments that have previously taken place.

Iron base super alloys are austenitic stainless steel modification. They are yet proprietory and manufactured via only single company. Austenitic steel is additionally alloyed along with some additional metals to generate super alloys. These alloying elements comprise Cobalt, W, Mo, V, Nb, Ti, Al, Zr, B and Copper. These super alloys are strengthened via strain hardening or via precipitation hardening. Such alloys are often utilized in between 650oC and 760oC, the range whether strain hardening effects are retained since addition of alloying elements raising recrystallization temperature to 925oC. The precipitation hardening is achieved because of precipitation of carbides nitrides of hard particles or boride that are stable above 750oC and thus super alloys are conveniently utilized in the range of 650oC-750oC.

Co and Nickel based super alloys have most of iron replaced via Co or Ni. These alloys can be hardened also by precipitation hardening or strain hardening. During precipitation in large size particles as 0.5 µ diameter made up of Ni3, Al or Ni3 Ti or their mixture are precipitated that are stable up to extremely high temperature. The utilizable temperature limit of these alloys is as high as 925oC.

Dispersion hardened alloys acquire their high temperature strength form finely dispersed ultrafine ceramic particles in the matrix of Ni. T. D. Nickel along with fine thoria or ThO2 dispersed in the matrix is possibly the only instance of that type. The material is extremely hard at room temperature and can't be deformed plastically. Still, it is very costly.

Posted Date: 2/27/2013 1:57:19 AM | Location : United States

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