Amorphization and nanoscale refinement of high nitrogen containing Fe-based crystalline materials by mechanical alloying

Mechanical alloying(MA) of elemental powder mixtures, with Fe-9.85mass%N alloy powders as the nitrogen source, of Fe 100 x-y A r N x (at.%)(A=Co,Cr,Nb,Ta,etc.; x=3-25; y=0-25) materials and stainless steel type materials such as Fe 87 x-y Cr 13 A y N x (at.%) (type 405)(A=Nb,Ta; x=3-25; y=0-5) and Fe 74 x-y Cr 18 Ni 8 A y N x (at.%)(type 304) (A=Nb,Ta; x=0-20; y=0-15) was performed in an argon atomosphere using a planetary ball mill. In the MA processing of the Fe-A-N materials, the additives A such as Nb, Ta, and Cr with the negative values of W AN markedly enhance the solid-state reactions in MA powder products, leading to amorphization of the MA powders after 720ks of processing, in contrast to the additive Co with the positive value of W AN ; the parameter W AN represents the difference in bonding energy of A-N atomic pairs (U AN ) and Fe-N pairs (U FeN ) in the ternary Fe-A-N solutions, i.e. W AN =U AN -U FeN . In addition, refinement of the ternary crystalline materials with the addtive clement like Ta or Nb was strongly promoted during MA for 360-720ks and the grain size of MA powders reduced to ca. 2-3nm before the crystalline-to-amorphous transition occurs. Such effects of additive elements on amorphization and refinement of MA materials seen in the ternary Fe-A-N systems also held for MA of high nitrogen containing stainless stcel type powder materials.