Peak Stir Zone Temperatures during Friction Stir Processing

The stir zone (SZ) temperature cycle was measured during the friction stir processing (FSP) of NiAl bronze plates. The FSP was conducted using a tool design with a smooth concave shoulder and a 12.7-mm step-spiral pin. Temperature sensing was accomplished using sheathed thermocouples embedded in the tool path within the plates, while simultaneous optical pyrometry measurements of surface temperatures were also obtained. Peak SZ temperatures were 990 ⁰Cto 1015 ⁰C (0.90 to 0.97 TMelt) and were not affected by preheating to 400⁰C, although the dwell time above 900 ⁰C was increased by the preheating. Thermocouple data suggested little variation in peak temperature across the SZ, although thermocouples initially located on the advancing sides and at the centerlines of the tool traverses were displaced to the retreating sides, precluding direct assessment of the temperature variation across the SZ. Microstructure-based estimates of local peak SZ temperatures have been made on these and on other similarly processed materials. Altogether, the peak-temperature determinations from these different measurement techniques are in close agreement

Optimization of the Strength-Fracture Toughness Relation in Particulate-Reinforced Aluminum Composites via Control of the Matrix Microstructure

The article of record as published may be found at http://dx.doi.org/10.1007/s11661-998-0119-9The evolution of the microstructure and mechanical properties of a 17.5 vol. pct SiC particulatereinforced aluminum alloy 6092-matrix composite has been studied as a function of postfabrication processing and heat treatment. It is demonstrated that, by the control of particulate distribution, matrix grain, and substructure and of the matrix precipitate state, the strength-toughness combination in the composite can be optimized over a wide range of properties, without resorting to unstable, underaged (UA) matrix microstructures, which are usually deemed necessary to produce a higher fracture toughness than that displayed in the peak-aged condition. Further, it is demonstrated that, following an appropriate combination of thermomechanical processing and unconventional heat treatment, the composite may possess better stiffness, strength, and fracture toughness than a similar unreinforced alloy. In the high- and low-strength matrix microstructural conditions, the matrix grain and substructure were found to play a substantial role in determining fracture properties. However, in the intermediate- strength regime, properties appeared to be optimizable by the utilization of heat treatments only. These observations are rationalized on the basis of current understanding of the grain size dependence of fracture toughness and the detailed microstructural features resulting from thermomechanical treatments.United States Army Research OfficeArmy Research LabratoryUnited States Air Force Office of Scientific ResearchWright Materials LabratoryDWA Composite

Friction stir processing (FSP): refining microstructures and improving properties

The article of record as published may be found at http://dx.doi.org/10.3989/revmetalmadrid.19XIIPMSFSP is reviewed as an allied technology of friction stir welding (FSW) and additional considerations such as processing pattern and step over distance are introduced. The application of FSP to continuously cast AA5083 material in the as-cast condition is described and the extent of grain refinement and homogenization of microstructure is documented. The FSP-induced superplastic response of this material is compared to the response of conventionally processed AA5083 and the improved ductility of the FSP material is related to grain refinement and microstructure homogenization

Estimation of martensite carbon content in as-quenched AISI 52100 steel by X-ray diffraction

The article of record as published may be found at http://dx.doi.org/10.1016/0167-577X(86)90100-XOverlapping martensite doublets have been resolved by approximating each component peak by a Pearson VII function. The Bragg angle difference between the component peaks of the resolved doublet is then used to calculate the carbon content of the martensite based on equations originally proposed by Roberts. The analysis has been applied to both an as-received and thermomechanically processed 52100 steel, heat treated to an as-quenched condition, and the results are in good agreement with hardness and retained austenite data.Naval Postgraduate SchoolCSIR (India

Microstructure and microtexture development during friction stir processing of nickel aluminum bronze

The article of record as published may be found at http://dx.doi.org/10.1017/S143192761201016

Department of Mechanical and Astronautical Engineering Report (2004)

Includes: Overview of the department, research mission, curricula served, degrees granted, research trusts, faculty expertise, etc

High temperature texture strengthening in zinc

It is shown that the high temperature creep strength of polycrystalline zinc is a strong function of the texture developed in the material. Powder metallurgy extruded zinc exhibits creep rates that are about 50 to 100 times slower in logitudinal samples than in transverse samples in the temperature range from 0.45 to 0.95 Tm. Such large anisotropic effects have not been previously observed and the results obtained suggest a high potential for elevated temperature texture strenghtening of such materials....U.S. Office of Naval Researc

Friction stir processing (FSP) and superplasticity

FSP is an allied technology of friction stir welding (FSW). The development and applications of these technologies are reviewed and additional considerations such as processing pattern and step over distance between successive passes in FSP are discussed. The deformation field for a rotating and advancing tool is not symmetric about the axis of tool motion. Thus, various spiral patterns with step over distances less than the tool pin diameter result in replacement of advancing interfaces (tool tangential velocity and traversing speed add) retreating interfaces (tool tangential velocity and traversing speed subtract) and greater homogeneity of the resulting stir zone microstructures. Microstructures formed as a result FSP often exhibit refined and uniform distributions of non-deforming constituents as well as highly refined grain structures, and superplastic response following FSP of wrought 7XXX and 5XXX Al alloys has been achieved. The application of multi-pass FSP to cast metals, including continuously cast (CC) AA5083 and AA356 as well as a Na modified Al-7Si will be summarized and the conversion of as-cast microstructures to a wrought condition in the absence of external shape change will be shown. Grain refinement is the result of recrystallization during the rapid thermomechanical cycle of FSP. The mechanisms involved in homogenization of constituent particle distributions remains to be determined. The FSP-induced superplastic response of the AA5083 will be documented. In contrast, grain refinement in the Na modified Al-7Si alloy was insufficient to support superplasticity.General Motors CorporationOffice of Naval Researc