ABSTRACT
Protective coatings based on an Al-Al2O3 metal matrix composite (MMC) were sprayed using dynamic metallization (DM), a low-pressure cold spray variant. A series of samples approximately 1 mm in thickness were sprayed using different spray process parameters (temperature, velocity) and different feedstock powder compositions (Al, Zn, Al2O3). This resulted in MMCs of different phase compositions and slightly different physical conditions of coating formation. The through-thickness residual stresses that accumulate in coatings during the spray process were studied using neutron diffraction in all phases comprising the MMCs. The overall residual stress in the coating (macrostress) was compressive, which is in good agreement with the data on residual stress observed in other cold spray coatings, accumulating as a result of the peening process. However, due to the slightly elevated spray temperature characteristic of DM in comparison with other cold spray variants, thermal stresses are also present and play an equally important role in the accumulation of residual stress in each phase. Because of the multi-phase composition and thermal mismatch between the metal and ceramic components of the MMC, inter-phase microstresses also accumulate. A micro-mechanical explanation of the observed tensile microstress in Al/Zn versus compressive stress in Al2O3 is proposed.
ABSTRACT
Grounds for the procedure of laser projector safety assessment are given. The method allows to measure maximum intensity of diffused and diffusely reflected radiation of laser projectors, irrespective of graphic effects being used. It also makes it possible to standardize the procedure of laser safety assessment, laser devices being used to produce a show.
Subject(s)
Lasers/adverse effects , Risk Assessment/methods , Consumer Product Safety , Humans , Occupational HealthABSTRACT
Hygienic evaluation covered 11 laser projectors used for theater and entertainment events and providing laser demonstrations. Laser irradiation diffusely reflected from the screen and scattered beyond the limits of zone with laser danger was proved safe.
