Kinetics and mechanism of hardening of Mn-Pd alloys

Conclusions

• 1. We investigated the kinetics of hardening in manganese alloys quenched from the γ Mn region — the distinguishing characteristic is the exceedingly sharp increase of the hardness during the first minute of holding (1–10 min) at 450–500°C. The hardness peak after very short holding times is due to the formation of β₁ phase. With holding for longer times secondary hardening occurs due to precipitation of the hard and brittle α Mn phase.

• 2. The maximum hardness with holding for a short time is higher for the alloy with a large palladium content (30%), which is accompanied by the volume effect of the γ → α₁ + α Mn transformation.

• 3. The hardness of β₁ phase is relatively low and varies little with the tempering time.

• 4. The high hardness of Mn−Pd alloys after holding for a short time is evidently due to the particular condition of the β₁ phase at the time of precipitation from the γ Mn solid solution and the internal stresses that occur.

• 5. In the hardened condition the Mn−Pd alloy with 30% Pd is nonmagnetic, has a high modulus of elasticity, and has satisfactory corrosion resistance.