Creepové Porušování Slitiny MgY3Nd2Zn1Mn1 Lité Metodou Squeeze Casting

The paper deals with the creep damage of the alloy MgY3Nd2Zn1Mn1 prepared by squeeze casting. The tensile creep tests were performed at constant load in the stress range 30 to 80 MPa and at 300^oC. In the stress range 30 to 70 MPa, the minimum creep rate (ε/t)_min is a function of the stress which follows a power law with an exponent n = 5.89. The time to fracture t_f is also a power function of the stress with an exponent m = - 4.39. The modified Monkman-Grant relation can be expressed by the equation t_f/(ε_f − ε_p).(ε/t)_min^1.0001 = 0.57, where ε_f is the strain at fracture and ε_p is the strain of primary creep. Both the mean value of the modified Monkman-Grant and its scatter (determined for the particular stress values in the Monkman-Grant relation at unity value of the exponent) correspond to the model of constrained growth of cavities along dendrite boundaries. The creep damage consisting in initiation, growth and coalescence of cavities at dendrite boundaries was monitored by light microscopy observation of the surface of creep test pieces and metallographic samples prepared in planes parallel with test pieces axis, and by fractographic studies of fracture surfaces of broken creep specimens using scanning electron microscopy. In addition, our results proved the validity of the relation between the time to fracture t_f and the time necessary to achieve the Monkman-Grant elongation t_MGD= t_f.(ε/t)_min consistent with the model of continuous creep damage.