Localized Mechanical Characterization of Welded/Joined Materials
Quantitative Study of Material Joining Techniques
Understanding the joining of two solid surfaces bonded together is an active area of scientific research for both academia and industry. The ubiquitous use of material joining techniques and the various means by which materials can be joined: mechanically, physically, and chemically, offers endless avenues of interesting studies on a fundamental level. When engineering a bond between two materials, criteria such as service temperature, strength of bond, fatigue resistance, ability of materials to be joined, etc. contribute to the design. For present day engineering of joined materials, understanding localized mechanical properties from a microstructural perspective will lead to better control of processing techniques, ultimately driving the development of advanced joining materials with outstanding performance and reliability.
Nanoindentation of Joined Materials
Nanoindentation is a versatile technique used to measure localized mechanical properties rapidly and accurately for broad classes of materials. By combining environmental control and ease of sample mounting, nanoindentation is well suited to study the various dissimilar and vast materials used within material joining.
Mechanical Material Joining: Bolting, riveting, and clamping are familiar examples of mechanical fastening. Nanomechanical measurements may be conducted under controlled environments ranging from harsh oxidizing conditions to elevated temperatures. Hysitron’s electrochemical, gaseous, fluid, or temperature control options enable localized mechanical property measurements of mechanically fastened materials while replicating in-service conditions. Site specific mechanical characterization of pitting caused by localized corrosion attack in steel rivets submerged in seawater, or effects of intergranular corrosion on the nanomechanical behavior of a gusset plate would be two potential applications of nanomechanical characterization, among many.
Physical Material Joining: Bonding materials together by phase changes (i.e. crystallization from a melt), evaporation of solvents in glues, or diffusing two materials together are ways of physically joining materials. To better understand time and temperature influence on diffusion parameters from diffusion bonding, accurate and fast measurements of property gradients through diffusion zones may be conducted using spatial resolution provided by nanoindentation.
Chemical Material Joining: Chemical processes to join materials together involves the interaction of intermolecular forces (e.g. covalent bonds, van der Waals) between two materials. Implementing nanoindentation for pull-off force measurements of tacky resins used in pressure sensitive adhesives, or utilizing dynamic characterization to measure curing of epoxy resins at various temperatures are common applications.
Soldering or welding are traditional material joining techniques that can be categorized as a merge between physical and chemical bonding. When two metals are fused together by heat, the microstructure at the interface unavoidably changes producing alterations in mechanical behavior, and ultimately weld performance. Using nanomechanical characterization to investigate the extent of the heat affected zone from a weld, or measuring the mechanical integrity of lead-free solder bumps for microelectronics at elevated temperatures offer powerful insight for designing advanced materials.