Advanced Metallic Systems
Alloy development and process design for improved properties
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Microstructural Evolution from Ageing, Creep and Thermomechanical Fatigue in Lead Free Solders
Characterization and modeling of microstructural evolution due to thermomechanical fatigue in solder joints is investigated using several approaches. Currently we are using specially designed joints to facilitate observation and interrogation of the microstructure using scanning electron microscopy, orientation imaging microscopy (to map crystal orientations along with microstructure features) and nanoindentation. Recent reserach projects have included investigations into residual stress, stress relaxation, localized deformation during creep, and effects of reinforcements in composite solders manufactured by ex-situ and in-situ methods. This project is supported by a focused research group (Subramanian, Bieler, Lucas) grant from NSF (NSF-DMR-0081796), Visteon, and the Michigan State University Composite Materials and Research Center Current students: Honjoo Rhee (nano-indentation), Jong-Gi Lee (thermomechanical fatigue specimens), Adwait Telang (orientation imaging, reversed shear), Hairong Jaing (new) Students recently graduated: Sunlak Choi, Ph.D. (in-situ composite solder) Fu Guo, Ph.D. (ex-situ composite solder), Susheel Jadhav, M.S. (Stress-relaxation), Jeff McDougall (localized creep deformation)
Investigators (PI is linked): Thomas R. Bieler
Categories: Advanced Metallic Systems, Structural Materials, Electronic Materials
Effects of Heat Treatment on Primary Creep of TiAl
The effects of heat treatment on precipitation of carbide particles and their effect on primary creep and other mechanical properties is investigated using electron microscopy, microhardness and macrohardness measurements. Supported by Howmet Research Corp.
Investigators (PI is linked): Thomas R. Bieler
Categories: Advanced Metallic Systems, Structural Materials
Deformation Transfer and/or Fracture Initiation in Micro-lamellar TiAl
A scanning electron microscope technique that allows defects to be imaged in bulk specimens in a manner similar to TEM called electron channeling contrast imaging (ECCI) is used as a tool to examine the nature of deformation transfer at grain boundaries. In this study, a number of g-g grain boundaries in a TiAl alloy that display successful deformation transfer have been examined. Trace analysis based on selected area channeling patterns is used to characterize the active deformation systems in the grains on both sides of the boundaries. To interpret, and possibly predict, these observed patterns of strain accommodation/transfer at grain boundaries, a nonlinear variational model of plastic deformation in a bicrystal is being developed by D.E. Mason, in the ME department. Funded by AFOSR, grant number AFRL No. F49620-01-1-0116.
Investigators (PI is linked): Thomas R. Bieler
Categories: Advanced Metallic Systems, Structural Materials
High Temperature Shape Memory Alloy Development for Use above 500 C.
Shape memory alloys such as beta-NiTi can deliver large thermally-driven forces and displace-ments and are potentially useful in a range of aeropropulsion and MEMS actuator applications. Their use is, however, discouraged by a maximum operating temperature of about 100 C. This limitation is surmountable through the use of NiTiX alloys, with X = Hf (substituting for Ti), or Pd, Au or Pt, substitut-ing for nickel on the B2 superlattice. Our recent work on (Ti+Hf)Ni and Ti(Ni+Pd) has shown that good mechanical properties and excellent shape-memory can be obtained in these systems, with austenite-finish temperatures exceeding 240 C. Furthermore, alloys based on TiPt have transformation tempera-tures above 1000 C. Although little is presently known about this material, Ti50Ni20Pt30 should allow design of actuators for operation above 500 C. This NASA-funded project is directed at the development of this class of shape-active metals for application to MEMS, smart composite materials, and high-temperature shape-memory components for turbine engines.
Investigators (PI is linked): David S. Grummon
Categories: Advanced Metallic Systems
Imaging of Dislocations in Bulk SEM Samples
The deformation and fracture behavior of materials is being studied by examining near surface dislocations in bulk SEM samples using electron channeling contrast imaging (ECCI). This novel approach facilitates in-situ deformation studies under well defined stress states, while avoiding the complications associated with TEM thin films. Currently, dislocation are being imaged in intermetallic alloy in an effort to optimize deformation behavior. Dislocations processes at both crack tips and at grain boundaries are being studied.
Investigators (PI is linked): Martin A. Crimp
Categories: Advanced Metallic Systems, Structural Materials
Elevated-Temp Grain Boundary Deformation Processes of Structural Alloys: Grain Boundary Engineering
The lifetimes of metallic alloys under imposed thermo-mechanical loads are influenced by microstructure, and in particular the grain size and the orientation of one grain with respect to its neighbor grain. Using an electron microscopy technique, called orientation imaging microscopy (OIM) or electron backscatter diffraction (EBSD), we can determine the crystallographic orientations which form between grains at the grain boundaries. These orientations have an important influence on the mechanical behavior of alloys and in particular the high-temperature deformation or creep behavior. By altering the distribution of the grain boundary orientations [also referred to as changing the grain boundary character distribution (GBCD)] in a material’s microstructure using different thermomechanical processing techniques (involving different applied pressures and temperatures or “heat-it and beat-it” metallurgy), we can improve the deformation resistance of the material. Thus it is possible to exert control over the types of grain boundaries in the microstructure and thereby engineer properties. This technique is referred to as grain boundary engineering. The understanding gained through grain boundary engineering leads to processing techniques which can be tailored to obtain the desired mechanical properties for a given material’s application.
Investigators (PI is linked): Carl Boehlert
Categories: Advanced Metallic Systems, Structural Materials
Lead-Free Electronic Solders for Severe Service Conditions
Electronic solder joints present in modern microelectronics encounter several severe simultaneous fields during service. Severe fluctuations in temperatures causing thermomechanical fatigue, high current density causing electromigration, and mechanical stresses, encountered during service significantly affect the reliability of the electronic interconnects. In addition to their individual influences, synergistic interactions between them play significant roles. In tin based electronics, whisker growth and tin-pest resulting from phase transformation are also becoming long-term reliability concerns. Current focus of the project is to develop a fundamental understanding of these issues by carrying out detailed studies on microstructural evolution and its influence on the life of the electronic solder joints. The main aim of the project is to develop suitable models for reliability predictions, and arrive at appropriate solutions to combat such problems.
Investigators (PI is linked): K.N. Subramanian
Categories: Electronic Materials, Advanced Metallic Systems
Reducing defects in manufactured titanium fasteners
Fasteners made from Ti-6Al-4V occasionally show defects arising from the thread rolling process. This project seeks to identify the source and seriousness of these defects, so that they can be eliminated or minimized. A miniature fatigue stage to evaluate the impact of these defects on high cycle fatigue behavior is under development. Projected outcome will be to define the characteristics of a defect that can compromise performance. Supported by Fairchild Fasteners, City of Industry, CA.
Investigators (PI is linked): Thomas R. Bieler
Categories: Advanced Metallic Systems, Structural Materials
Thin Film Shape Memory Alloys on Polymeric Substrates for Microactuators
This work aims at development of very-low cost microactuator materials using sputtered thin film NiTi alloys as high-energy force-producing elements. The principa objective is to develop methods for web-coating of thin polyimide substrates with NiTi alloys. Deposition of NiTi onto refractory polymers such as DuPont Kapton, aside from allowing low-cost continuous processing of large surface areas, results in a composit film having a number of advantages. Whereas the NiTi shape-memory metallization stiffens and recovers a set shape when heated, the polyimide substrate responds to heating by becoming more compliant, and will tend to recover a set shape when it cools. The materials are thus compatible and highly complimentary, and will form the basis of an important class of extremely rugged microactuation materials capable of providing large forces and smooth displacement output, low-voltage operation, biocompatibility, and the ability to operate in liquids or in harsh environments.
Investigators (PI is linked): David S. Grummon
Categories: Advanced Metallic Systems
Development of Nanostructured Lead-free Solder
In order to improve the service performance of lead-free electronic solders a sub-micron size inert and stable reinforcement, that bonds extremely well and be present in grain boundary regions of the solder matrix without any agglomeration during processing or coarsening during additional exposure to service environments, is essential. Unluckily, traditionally evaluated approaches utilizing ceramic, metallic and IMC particulate reinforcements or alloying methodologies do not satisfy all these requirements. POSS-silanols containing one to three (Si-OH) groups consist of inert strongly bonded cage structure made of Si-O with surface active groups. As a consequence, the negatively charged -OH surface active groups present in POSS may strongly bond with the metallic matrix, hopefully to the grain boundary regions of the solder. The negatively charged surface active groups present on the surface of POSS should also prevent flocculation of these reinforcements during processing. Since bonding between Si and O is very strong, they will not dissociate in service environments. This will alleviate any coarsening problems that may be encountered during service.
Investigators (PI is linked): Andre Y. Lee
Categories: Nanomaterials, Electronic Materials, Advanced Metallic Systems
Radiation Effects on the Structure and Electronic Properties of Carbon Nanotubes
Traditional Si based electrons are susceptible to rapid degradation in space radiation environments, limiting their application in satellite and space exploration systems. Currently, carbon nanotubes are being developed for nanoscale electronic circuits. In this program, we are studying the stability of carbon nanotubes and nanotubes/metal contacts when exposed to high energy radiation. These structures are being irradiated with high energy (12,000 MeV) 86Kr ions, which simulate space radiation environments, in the National Superconducting Cyclotron Laboratory at Michigan State University. The irradiated structures are being characterized using high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) in order to determine the structural and electronic degradation as a function of exposure.
Investigators (PI is linked): Martin A. Crimp
Categories: Advanced Metallic Systems, Electronic Materials
Growth and Characterization of Rare-Earth Silicide Nanowires and Nanostructures
Self-assembled nanowires are potential structures for interconnects in nanoscale electronic applications. In this study, GdSi2, DySi2, and ScDy2 nanostructures are being grown on Si(100) substrates by evaporation/self assembly. Bulk coverages ranging from 0.3 to 3.0 monolayers of silicide result in a variety of morphologies and crystal structures. Large aspect ratio nanowires grow have been found to grow in <110>Si directions. Larger rectangular 3-D islands are also observed. The relationships between substrates, growth conditions, and nanostructure morphology and crystal structure are being characterized using scanning tunneling microscopy and advanced transmission electron microscopy techniques including HRTEM, convergent beam electron diffraction, and EELS.
Investigators (PI is linked): Martin A. Crimp
Categories: Advanced Metallic Systems, Electronic Materials
Nitinol Brazing
This project concerns development of a novel joining technique for Nitinol shape-memory and superelastic alloys, recently discovered at MSU in collaboration with John A. Shaw at the University of Michigan Dept. of Aerospace Engineering. Using pure niobium as a melting point depressant, the method produces a highly robust and biocompatible metallurgical bond between NiTi sections. Detailed studies on thermodynamics of the Ni-Ti-Nb ternary system and the kinetics of contact melting in NiTi-Nb couples are underway. Experimental work on the use of the approach in resistance welding, metal-inert gas welding, vacuum brazing, and the joining of sputtered thin films sections are being conducted. A sputtered multilayer brazing foil has been developed which solves long-standing problems associated with metallurgical joining in this important alloy system.
Investigators (PI is linked): David S. Grummon
Categories: Advanced Metallic Systems
Functional Superelastic Interlayers for Control of Friction and Wear in Hard-Coated Components
This project, funded by NSF under the GOALI program and carried out in collaboration with General Motors Corp., exploits superelastic deformation in sputtered NiTi interlayers, integrated with conventional CrN and DLC hard coatings, to limit substrate damage and reduce contact stresses during dry sliding wear processes. Superelastic interlayers have been observed to improve the performance of hard coatings by more than two orders of magnitude as measured in wear loss studies.
Investigators (PI is linked): David S. Grummon
Categories: Advanced Metallic Systems
Development of In-Situ Electron-Microscopy Techniques
This research has three main goals. The first thrust is to develop a technique to combine in-situ deformation observations with in-situ electron backscattered diffraction observations of metallic alloy specimens inside the chamber of a scanning electron microscope. The second area is to identify phase transformations using in-situ observations of metallic alloys using a heating stage within an electron microscope. The third area would be to combine the heating capability of the stage with the loading capability of the stage to perform in-situ deformation observations of metallic alloy specimens during isothermal fatigue, thermomechanical fatigue, creep, and fatigue-creep interactions at elevated temperatures.
Investigators (PI is linked): Carl Boehlert
Categories: Advanced Metallic Systems, Structural Materials
The Effect of Boron the Creep and Fatigue Behavior of Ti-6Al-4V(wt.%)
The objectives of this program are to access the effects of B additions (0, 0.1, and 1wt.%) on the creep strain-life behavior of Ti-6Al-4V(wt.%), to understand and evaluate the creep deformation mechanisms of Ti-6Al-4VB-xB(wt.%) as a function of stress and temperature, and to evaluate the creep deformation evolution as a function of stress, temperature, time, and strain using in-situ surface observations. Constant-load creep experiments will be performed and post-experiment SEM and TEM analysis of the deformed gage sections will be evaluated. The test matrix will involve experiments performed at temperatures ranging between 400-455C and stresses ranging between 400-6500MPa. Such experiments will last up to 800 hours based on previously reported data of Ti-64 [Materials Property Handbook: Titanium Alloys, Boyer, Welsch, Collings (1994) ASM Intl., pp.530-532]. In addition, load-jump and temperature-jump experiments will be performed to evaluate the creep parameters, n and Q, for a cursory prediction of the suggested dominant secondary-creep-stage deformation mechanisms based on creep of pure metals. This type of evaluation will be supplemented by experiments performed in-situ in an SEM chamber. Such specimens will be metallographically polished prior to testing in order to image the surfaces at certain stages of creep strain using an Ernest-Fullam tensile stage. Such experiments will be performed at identical temperatures and stresses as those to be performed in the conventional creep experiments using the lever-arm creep frames. The in-situ testing will be used to accomplish the third objective. It is noted that a few of the conventional experiments will be performed in a vacuum environment (5x10-8 torr) in order to evaluate the effect of environment on the creep response.
Investigators (PI is linked): Carl Boehlert
Categories: Advanced Metallic Systems, Structural Materials