Preparation Of Nonstoichiometric Crn_x By Ma And Its Sintering Characteristric

Chromium nitride (CrN) are widely used because they possess many excellent physical and chemical properties. Like the high wear resistance, antiferromagnetism which other transition metal don't possess and the properties of decomposeing high activity nitrogen (N₂) when it's heaten. Nevertheless, preparing CrN is very difficult because of the low activity of Cr, and because of its high brittleness, study of sintering samples is very little, either. Therefore, simplifying the preparation of CrN is an issue for the widely application of refractory compounds. The CrN_x powders fabricated by means of MA were sintered by SPS. The sintered samples possess excellent mechanical properties.The mixed powders of Cr₂N and Cr were mechanical alloyed to synthesize nonstoichiometric CrN_x. An X-ray diffractometer (XRD) and a sanning electron microscope (SEM) were used to analyze the structures and observe the morphologies of the milled powders. A differential scanning calorimetry (DSC) was used to analyze the structure of the mixed powders after being heaten up.The CrN_x powder fabricated by means of MA was sintered at different temperature under vacuum and at the pressure of 20 MPa. The fracture surfaces of the sintered samples were investigated by SEM and the mechanical properties were tested.The results of structure analyze of mixed powders showed that with the Cr content increased ,the grain size of CrN_x was increaseand at first then decreased and the change of N₂ content which was been decomposed after heaten was the same under the condition of same MA time. with the MA time increased ,the grain size of CrN_x was decreased gradually and the change of N₂ content which was been decomposed after being heaten up was decreased under the condition of same proportion of rough material. The result of SEM showed that with the Cr content increased ,the degree of aggregation of the MAed powders was increased ,and the granularity were increase at first, then decreased under the condition of same MA time; with the MA time increased , the granularity was decreased gradually then reach the balance finally under the condition of same proportion of raw material. The results of structure analyze and mechanical properties of the sintered samples showed that as sintering temperature increased, the grain size of the sintering samples was decreases, desity, microhardness, breaking strength were increased. The mechanical properties for the sintering sample of the Cr₂N and Cr powders mixed as 1:0.5 molar ratio milled for 50h are optimum. The desity, microhardness, and rupture strength are 22.09GPa, 99.5% and 239.1MPa.