Mo 2 Ga 2 C, a double-A-layer MAX, is reported to be films or powders. This paper researched the sintering properties of M 2 Ga 2 C powders to make dense bulk samples by vacuum hot pressing. It was found that 750 ℃ was a suitable sintering temperature, while higher temperature (850 ℃) resulted in decomposition of Mo 2 Ga 2 C yielding to main product of Mo 2 C. During sintering process at 750 ℃, its grain size did not increase obviously with sintering time, meanwhile the size of pores decreased markedly and the relative density increased significantly with the increasing sintering time. Additionally, the hot-pressed samples had obvious texture. Due to layering, some grains changed their orientations during sintering, of which most of the (00l) planes in the hot-pressed samples preferred to be perpendicular to the direction of hot press. Almost fully densed Mo 2 Ga 2 C bulk (relative density: 98.8%) was obtained by hot pressing at 750 ℃ for 8 h. This advantage of the method suggested that it can serve as a promising preparation for Mo 2 Ga 2 C, a double-A-Layer MAX.

To solve the debonding and fracture problems caused by the different thermal expansion coefficients of the transducer element and the measured object, a new method combined with the powder lamination, pressureless infiltration and hot pressing sintering is proposed to prepare Fe/PZT functionally graded material as the matching layer of transducers. The microstructure and element distribution of the functionally graded layer are analyzed by the SEM and EDS. The results show that the volume fraction and elements of the functionally graded layer after the pressureless infiltration at 1100 °C and the hot pressing at 800 °C are linearly and continuously distributed along the thickness direction. The thermal cycle contrast test shows the well matching performance of the functionally graded disk as the transducer matching layer from room temperature to 180 °C. Finally, Lamb wave propagation experiment at the 180 °C shows that the functionally graded matching layer can be used effectively.