  In this work the global and local mechanical properties of the magnetocaloric
intermetallic LaFe11.2Si1.8 alloy are investigated by a combination of
different testing and characterization techniques in order to shed light on the
partly contradictory data in recent literature. Macroscale compression tests
were performed to illuminate the global fracture behavior and evaluate it
statistically. LaFe11.2Si1.8 demonstrates a brittle behavior with fracture
strains below 0.6 % and widely distributed fracture stresses of 180-620 MPa
leading to a Weibull modulus of m = 2 to 6. The local mechanical properties,
such as hardness and Youngs modulus, of the main and secondary phases are
examined by nanoindentation and Vickers microhardness tests. An intrinsic
strength of the main magnetocaloric phase of at least 2 GPa is estimated. The
significantly lower values obtained by compression tests are attributed to the
detrimental effect of pores, microcracks, and secondary phases. Microscopic
examination of indentation-induced cracks reveals that ductile alpha-Fe
precipitates act as crack arrestors whereas pre-existing cracks at La-rich
precipitates provide numerous "weak links" for the initiation of catastrophic
fracture. The presented systematic study extends the understanding of the
mechanical reliability of La(Fe, Si)13 alloys by revealing the correlations
between the mechanical behavior of macroscopic multi-phase samples and the
local mechanical properties of the single phases.

Materials Science