Transition-metal carbides are often used as sintering additives in ZrB2-and HfB2-based ultra-high temperature ceramic(UHTC)composites to reach full densification,and they also help to remove oxide impurities that degrade the high temperature performance.By employing quantitative TEM and SEM analysis to measure solute distribution and microstructure in combination with XRD refinements,actual phase composition and phase component were obtained in three UHTC systems densified by reactive sintering,pressureless sintering and hot-pressing,respectively.