The influence of surface roughness and pre-oxidation state on the wettability of aluminium nitride by commercial brazes

The effects of roughness (Ra = 0.17–0.20 m) and of pre-oxidation of the AlN ceramic surface on its wettability and contact interaction with commercial brazing alloys CB4 and CB5 of Ag-Cu-Ti composition have been studied. Wettability has been determined by the sessile drop method at three holding temperatures (810, 900 and 950°C). Particularities of the interface interaction have been identified by microprobe analysis for pre-oxidized samples. Experimental data are compared with data for samples polished to Ra = 0.02–0.03 m not subjected to pre-oxidation. The results show that, for the systems under study, surface roughness does not influence the contact angle value significantly. Pre-oxidation of the AlN in air at 1250°C, however, tends to reduce wettability as a result of the replacement of braze-aluminium nitride interaction by braze-surface aluminium oxide interaction.     

Ge–Al and Sn–Al alloys capillary properties in contact with aluminum nitride

Experimental isotherms are presented for (1) wettability of AlN ceramics by Ge–Al and Sn–Al alloys, (2) surface tension and density of Ge–Al and Sn–Al alloys in the whole concentration range. Complex consideration of capillary characteristics of the melts under study is performed taking into account data available on thermodynamic activities of the melt components. The contact angle isotherms pass the minimum point for both systems. The contact angle value drops with Al addition more sharply for the Sn–Al system than for the Ge–Al alloys. This is in qualitative agreement with the higher thermodynamic activity of the components of the Sn–Al alloys. Sn decreases Al surface tension more than Ge. The reason for this is not only lower surface tension of Sn as compared to Ge, but also the higher thermodynamic activity of Sn in the Al melt.     

Wettability of aluminium nitride by tin–aluminium melts

The wettability of aluminium nitride by Sn–Al melts was studied by the sessile drop method in a vaccum of 2 × 10^–3 Pa at 1100 °C over the whole concentration region. The minimum interval on the contact-angle concentration dependence curve was observed at intermediate composition. For comparison, experiments were also performed on porous AlN. Wetting of porous nitride is worse than the dense nitride. The results have been analysed on the basis of the relation between wettability and the chemical interface reactivity in solid–liquid metal systems.