No abstract

The ballistic performance of state‐of‐the‐art silicon carbide armor material can exhibit a fairly wide variability in certain test configurations, which, it is proposed, may be due to the presence of large (>0.1 mm), rare defects, termed, herein, “anomalous” defects. SiC rubble resulting from ballistic tests was examined, as were quasi‐static test samples. Ballistic fragment fracture surfaces revealed large carbonaceous defects that seemed to affect fracture path and mode. Low‐strength biaxial flexure samples demonstrated similar defects (>0.1 mm) as failure origins. Carbonaceous defects similar in appearance but smaller in size were also found at the fracture origins of SiC bend bars. Frequently, alumina inclusions were found within the carbonaceous discontinuities. These alumina inclusions may cause the graphitic regions to form during sintering. The random distribution of such large, rare carbonaceous discontinuities from sample‐to‐sample, as well as batch‐to‐batch variability, may explain high ballistic variability for SiC armor ceramics.

No abstract

Use of aluminum oxynitride (AlON) in transparent armor systems has been difficult due to the expense and limitations of the processing methods currently necessary to achieve transparency. Development of a pressureless processing method based on direct reaction sintering of alumina and aluminum nitride powders would reduce costs and provide a more flexible and practical manufacturing method. It may be possible to develop such a processing method using liquid phase sintering; as long as the liquid phase does not remain in the final sample. AlPO 4 forms a liquid phase with Al 2 O 3 and AlN at the temperatures required to sinter AlON, and slowly decomposes into P 2 O 5 and alumina. Therefore, it was investigated as a possible transient liquid phase for reaction-sintered AlON. Small compacts of alumina and aluminum nitride with up to of 15.0 wt% AlPO 4 additive were pressed and sintered. It was found that AlPO 4 formed the requisite transient liquid phase, and it was possible to adjust the process to produce AlON samples with good transmission and densities of 3.66-3.67 g/cc. XRD confirmed the samples formed were AlON, with no trace of any remaining phosphate phases or excess alumina or aluminum nitride. Based on the results, it was concluded that AlPO 4 could be utilized as a transient liquid phase to improve the density and transmission of AlON produced by pressureless reaction sintering.