18.Boronizing is performed on various material including tool steels, Ni - and Co-based alloys, as wee as plain carbon steels to obtain thin casing with(1 Point) a. High hardness (70HRC) b. High abrasion resistance c. a and b in addition to improved corrosion resistance and low coefficient of friction 19.Gas nitriding is applied to steel parts in an atmosphere of ammonia ( NH3 ) or other nitrogen-rich gas mixture is carried out at (1 Point) c. 1200C 20.Among the various types of material, the ones requiring least energy to shape are(1 Point) a. Metals b. Plastics c. Ceramics 21. Heating the steel into the austenite phase region and soaking followed by "air cooling" to room temperature results(1 Point) a. Fine pearlite (higher strength and hardness) b. Coarse pearlite (lower strength) c. Stress relief 22.Thermosetting polymers, if reheated they(1 Point) a. Soften b. Melt c. Degrade and char