Deformation behavior and joining of a MgF_2 optical ceramic

摘要

Compressive deformation behavior of a polycrystalline magnesium fluoride (MgF_2) ceramic was investigated at temperatures ranging from 760 to 830 deg C in an argon atmosphere at strain rates between 2 X 10~(-6) and 4 X 10~(-5) s~(-1). Steady-state flow stresses increased with increasing strain rates and ranged between 2 and 38 MPa. Stress exponents of approx = 1.4 + - 0.2 were determined at temperatures >760 deg C, indicative of a viscous diffusion-controlled deformation mechanism. Activation energy, determined from flow stress as a function of temperature, at a constant strain rate, was approx = 476 + - 60 kJ/mol. Self-joining by plastic deformation of MgF_2 was demonstrated at 830 deg C at a strain rate of 5 X 10~(-6) s~(-1). The joined samples were characterized by optical transmission measurements and their transmittivity was approx = 80 percent of the unjoined sample in the 2.5-8 mu m wavelength range.