Deformation behavior and joining of a MgF2 optical ceramic

Compressive deformation behavior of a polycrystalline magnesium fluoride (MgF2) ceramic was investigated at temperatures ranging from 760 to 830 °C in an argon atmosphere at strain rates between 2 × 10−6 and 4 × 10−5 s−1. Steady-state flow stresses increased with increasing strain rates and ranged between 2 and 38 MPa. Stress exponents of ≈1.4 ± 0.2 were determined at temperatures >760 °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 ≈476 ± 60 kJ/mol. Self-joining by plastic deformation of MgF2 was demonstrated at 830 °C at a strain rate of 5 × 10−6 s−1. The joined samples were characterized by optical transmission measurements and their transmittivity was ≈80% of the unjoined sample in the 2.5–8 μm wavelength range.