Essential Factors Influencing the Bonding Strength of Cold-Sprayed Aluminum Coatings on Ceramic Substrates
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Essential Factors Influencing the Bonding Strength of ColdSprayed Aluminum Coatings on Ceramic Substrates R. Drehmann1 • T. Grund1 • T. Lampke1 • B. Wielage1 • C. Wu¨stefeld2 M. Motylenko2 • D. Rafaja2
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Submitted: 17 July 2017 / in revised form: 2 December 2017 Ó ASM International 2018
Abstract The present work summarizes the most important results of a research project dealing with the comprehensive investigation of the bonding mechanisms between cold-sprayed Al coatings and various poly- and monocrystalline ceramic substrates (Al2O3, AlN, Si3N4, SiC, MgF2). Due to their exceptional combination of properties, metallized ceramics are gaining more and more importance for a wide variety of applications, especially in electronic engineering. Cold spray provides a quick, flexible, and cost-effective one-step process to apply metallic coatings on ceramic surfaces. However, since most of the existing cold-spray-related publications focus on metallic substrates, only very little is known about the bonding mechanisms acting between cold-sprayed metals and ceramic substrates. In this paper, the essential factors influencing the bonding strength in such composites are identified. Besides mechanical tensile strength testing, a thorough analysis of the coatings and especially the metal/ ceramic interfaces was conducted by means of HRTEM, FFT, STEM, EDX, EELS, GAXRD, and EBSD. The influence of substrate material, substrate temperature, and particle size is evaluated. The results suggest that, apart from mechanical interlocking, the adhesion of cold-sprayed
This article is an invited paper selected from presentations at the 2017 International Thermal Spray Conference, held June 7-9, 2017, in Du¨sseldorf, Germany, that has been expanded from the original presentation. & R. Drehmann [email protected] 1
Institute of Materials Science and Engineering, Chemnitz University of Technology, Chemnitz, Germany
2
Institute of Materials Science, Technische Universita¨t Bergakademie Freiberg, Freiberg, Germany
metallic coatings on ceramics is based on a complex interplay of different mechanisms such as quasiadiabatic shearing, static recrystallization, and heteroepitaxial growth. Keywords adhesion aluminum ceramics cold gas spraying (CGS) heteroepitaxy HRTEM tensile bond strength
Introduction The deposition of metallic coatings on ceramic surfaces is the precondition for various practical applications, especially in electronic engineering. Metal/ceramic compounds with good interfacial bonding are for instance needed in insulated-gate bipolar transistors (IGBTs), metal–oxide– semiconductor field-effect transistors (MOSFETs), and similar conductive structures on electrically isolating materials (Ref 1-4). However, due to the significant differences in the properties of substrate and coating material, the metallization of ceramics is often still a challenge. Thus, the conventional processes to produce metallized ceramics such as direct copper bonding, active metal brazing, CVD, PVD, or W/Mn meta
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