Fracture Properties and Residual Stresses in Small Dimensions: Interface Dominated Fracture
Sponsored by: TMS Structural Materials Division, TMS Materials Processing and Manufacturing Division, TMS: Mechanical Behavior of Materials Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Daniel Kiener, University of Leoben; Marco Sebastiani, Roma TRE university; Nagamani Jaya Balila, Max Planck Institut fuer Eisenforschung GmbH; William Gerberich, University of Minnesota; Siddhartha (Sid) Pathak, University of Nevada, Reno

Thursday 2:00 PM
March 2, 2017
Room: 21
Location: San Diego Convention Ctr

Session Chair: Rafael Soler, MPIE; Nan Li, Los Alamos National Laboratory

2:00 PM  Invited
Temperature-Dependent Delamination Failure of Metal-Ceramic Interfaces: Rafael Soler1; Sriram Venkatesan1; Johannes Zechner2; Michael Nelhiebel2; Roman Roth3; Josef Fugger2; Gerhard Dehm1; 1Max-Planck-Institut für Eisenforschung GmbH; 2KAI - Kompetenzzentrum Automobil- und Industrieelektronik; 3Infineon Technologies AG
    Delamination failure in modern microelectronic devices, where complex multi-layered structures are common, is known to be usually driven by thermal expansion mismatch stresses, both produced during the thin film fabrication process and during device operation (where multiple loading condition, e.g. temporal and spatial temperature gradients, are induced). In this work we shed some light on the delamination behavior of such complex structures under service temperatures, i.e. up to 400 °C. We analyse the temperature dependency on the interface strength of bimaterial interfaces. The study focuses on various metal-ceramic interfaces, namely between a metallization layer (W, Ti, or Cu) and a borophosphosilicate glass (BPSG). The mechanical experiments are conducted by both, macro- and micro-scale approaches, i.e. 4-point-bending and single beam cantilever experiments, respectively. The temperature-dependent delamination behavior will be discussed with respect to the microstructural and chemical evolution from pre- and post-mortem samples.

2:30 PM  
Oxide-induced Substrate Cracking in Ti and Stainless Steels Driven by Pulsed Laser Irradiation: Jesus Morales Espejo1; David Bahr1; 1Purdue University
    Oxide layers grown on Ti6Al4V and 304 stainless steel using pulsed laser irradiation (PLI) at different scan rates on samples were analyzed. These oxides exhibit mudflat cracking, with an increasing crack density formed at faster laser scan rates. The mudflat cracks penetrate into the substrate of both materials, with crack depths between 1 – 6 μm. The cracks do not appear to be significantly influenced by the underlying substrate grain orientation. Residual stresses in the oxides were estimated using several methods. With the elastic and fracture properties of film measured using nanoindentation, a low substrate toughness is inferred, likely due to embrittlement promoted by hydrogen penetrating into the film and substrate during oxide growth; compositional depth profiles were carried out to explain this behavior. An understanding of the cracking phenomenon induced by PLI on both materials and possible mitigation mechanisms will be presented.

2:50 PM  
Fracture Toughness of Beryllium Using Insitu X-ray and Digital Image Correlation Techniques: Carl Cady1; Cheng Liu1; George Gray1; Neil Bourne2; 1Los Alamos National Laboratory; 2University of Manchester
    The primary reason for this investigation was to measure the fracture toughness on beryllium and observe crack growth using in-situ an x-ray characterization technique and digital image correlation. The fracture toughness was evaluated by using a “compression-fracture” introduced by Sammis and Ashby. Two experimental techniques were used to captured deformation and damage. An in-situ x-ray tomography technique was used for the internal fracture processes and digital image correlation for the surface evaluation. The development of technique to evaluate strain fields using linear elastic fracture mechanics provides consistent results that are typical of the standard fracture toughness evaluation. Further development in the characterization using continuum mechanics has led to a solution that more closely resembled the standard compact tension problem. In this solution we have been able to extract the modulus values and Poisson’s ratio form the experimental analysis and make corrections to the solution that minimizes errors.

3:10 PM  
Improved Fracture Resistance of Brittle Molybdenum Thin Films on Polyimide with Stress Tailoring: Megan Cordill1; Tanja Jörg2; Oleksandr Glushko1; Robert Franz2; Jörg Winkler3; Christian Mitterer2; 1Erich Schmid Institute of Materials Science; 2Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben; 3Business Unit Coating, PLANSEE SE
    Molybdenum has emerged as the material of choice for electronic applications due to its high thermal stability, chemical inertness, and low electrical resistance. Recently attention has been focused on the fracture behavior of these brittle thin films on polymers and their utilization in flexible electronics. This study reports on magnetron sputter deposited molybdenum films on polyimide substrates and how the residual stress of the thin films can be tailored to control the electro-mechanical behavior. In-situ characterization techniques were used to examine the mechanical and electrical response of the films during straining. Tensile tests were performed with in-situ resistance and x-ray diffraction measurements to determine the fracture strain of the films, while the crack evolution during straining was investigated with optical microscopy. In general, a high compressive stress state enabled the Mo films to withstand much higher tensile strains before the loss of conductivity and severe cracking occurred.

3:30 PM Break

3:50 PM  Invited
Enhanced Fracture Toughness of Mg/Nb Laminated Composites: Nan Li1; Youxing Chen1; Siddhartha Pathak2; Jian Wang3; Jon Baldwin1; Amit Misra4; Nathan Mara1; 1Los Alamos National Laboratory; 2University of Nevada, Reno; 3University of Nebraska-Lincoln; 4University of Michigan, Ann Arbor
    Enhancing fracture toughness of Mg alloys has been actively investigated due to its huge potential as structural materials in the aerospace and automotive industries. However, Mg and its alloys, with a hexagonal close packed structure, present lacked ductility and poor deformability. Therefore, it is still challenging to improve the deformability while maintaining the high flow strength of Mg and Mg alloys. Here, we propose to use Mg/Nb laminated composites to enhance the fracture toughness, in which a high density of interfaces are designed and manufactured to enhance both the yield strength and ductility. The mechanical strength of the Mg/Nb multilayers measured from pillar compression achieve a high value of ~1.1 GPa. In situ three-point bending experiments have been performed in a SEM. Mg/Nb interfaces play a dominant role to block crack propagation and blunt crack tip.

4:20 PM  
The Surface Residual Stress of High-frequency Induction Brazing of Cemented Carbide to Alloy Steel: Jia Ju1; Zhuang Liu1; Shuting Lou1; Ting Ruan1; 1Nanjing Institute of Technology
    Cemented carbide (WC-Co, YG8) and alloy steel (42CrMo) brazed with Cu-Zn-Ni-Mn filler metal was conducted via a high-frequency induction brazing method. The relationship between the brazing condition and surface residual stress in the joint interface were studied in detail. Welded joints have large surface residual stress because of the huge difference between the thermal expansion coefficients of welded materials. The surface residual stress in WC-Co and 42CrMo was declined as the heating/cooling rate decreased. Meanwhile, the maximum surface residual stress distribution is near the seam. The surface residual stress was declined when the distance to the weld seam increased. After welding, the surface residual stress has a big drop from more than 800 MPa, 300 MPa to less than 100 MPa, 72 MPa in WC-Co and 42CrMo side after tempering in low temperature respectively.

4:40 PM Concluding Comments