Study On The Processing And Mechanics In Double Partial Transient Liquid Phase Bonding Of Si₃N₄

Partial transient liquid-phase (PTLP) bonding as well as double PTLP bonding of Si₃N₄ ceramic were carried out in the present work by using Ti/Cu/Ti multi-interlayers and Ti/Cu/Ni/Cu/Ti multi-interlayers, respectively. The effects of interlayer thickness and bonding parameters on interfacial microstructure, reaction layer growing and element distribution as well as the joint strength have been systematically investigated. In addition, kinetics of PTLP bonding process has also been studied. Based on the experiment results, a numerical model for optimizing PTLP bonding parameters in PTLP bonding of Si₃N₄ ceramics to achieve best mechanical properties was established.The joint interfacial microstructure showed a layered structure of Si₃N₄/TiN (reaction layer)/Ti-Si compounds/Cu-Ti solid solution /Cu after PTLP bonding when Ti/Cu/Ti multi-interlayers was employed. The thickness of both the reaction layer and the Cu-Ti layer increased with the increasing in thickness of Ti interlayer. When the thickness of Ti interlayer exceeded a critical one, the Ti-Si compounds layer began to thicken and the joint strength was reduced due to the brittleness of Ti-Si compounds layer formed. The experiment results demonstrated that the joint strength was low with a thinner Ti interlayer due to the formation of a non-continuous reaction layer; whereas too thick a Ti interlayer also resulted in a low strength because of the formation of thick brittle reaction layer. The strength of joint PTLP bonded with Ti/Cu/Ti multi-interlayers measured at room temperature was 210MPa when following bonding parameters were used: bonding temperature 1050℃, holding time 3h, Ti interlayer 10μm and Cu interlayer 250μm.Investigation of kinetics associated with Si₃N₄/Ti/Cu/Ti/Si₃N₄ PTLP bonding process demonstrated that the growth of interface reaction layer obeyed the parabola law governed by the diffusion of participating elements. The growth coefficient k₁ at bonding temperature of 1323K was determined to be 9.234×10^-8m/s^1/2; the corresponding activation energy of growth was 87.2kJ/mol between the temperature 1283K and1343K.The thickness of isothermally solidified layer, ξ , and the isothermal solidification time, t, also obeyed the parabola equation. The isothermal solidification velocity coefficient k₂ was determined to be 1.5 ×10^-7 m/s^1/2. During the PTLP bonding process, both processes of the reaction layer growth and the liquid phase isothermal...