Optimizing superplastic response in lithium containing aluminum-magnesium alloys.

http://archive.org/details/optimizingsuperp00munrNAN

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

Materials research at NPS

Metals are useful partly because they can bend permanently before they break, i.e. they can deform plastically. Metal plasticity is usually evaluated by measurement of the percentage elongation during tensile testing and the result is referred to as the ductility of the material. Ductility of structural metals is typically 10-50% at ambient temperature and perhaps attains 100% at elevated temperatures

Thermomechanical processing of Al alloy 2090 for grain refinement and superplasticity.

http://archive.org/details/thermomechanical00spirNAN

Processing, deformation and failure in superplastic aluminum alloys: applications of orientation-imaging microscopy

The article of record as published may be found at http://dx.doi.org/10. 1361/10599490421349The importance of grain size refinement in enabling superplasticity is reviewed, and the current understanding of grain boundary characteristics is summarized. The application of orientation-imaging micros- copy (OIM) methods to the processing response and the deformation and failure modes in superplastic aluminum alloys are illustrated through microtexture analysis and determination of grain boundary characteristics in selected commercial materials. Continuous and discontinuous recrystallization reactions exhibit distinct microtextures and grain boundary characteristics. The application of OIM and microtexture analysis to the evaluation of both deformation and failure mechanisms during superplastic forming is illustrated

Amicrostructure - processing relationships in friction stir processing (FSP) of NiAl Bronze

The evolution of SZ and thermomechanically affected zone (TMAZ) microstructures during single-pass and multi-pass FSP by rectangular and spiral raster processes will be summarized. Microstructures produced by thermomechanical simulations will be compared to those produced during FSP. The distortion of microstructure constituents in thermomechanical simulations may be applied to estimation of SZ and TMAZ strain distributions in the initial FSP pass. Recrystallization in the primary α constituent is initiated at κiv (Fe3Al) particles prior to their dissolution during straining

Evolution of stir zone microstructure during FSP of cast NiAI bronze

Yutaka Sato, Yuri Hovanski, and Ravi Verma TMS (The Minerals, Metals & Materials Society), 2011The article of record as published may be located at http://dx.doi.org/10.1002/9781118062302.ch12The evolution of the stir zone microstructure during single-pass and multi-pass 'FSP of an as-cast NiAl bronze material was evaluated by optical and high-resolution scanning electron microscopy (SEM) methods, including orientation imaging microscopy (OIM). Deformation commences ahead of the tool as the local temperature exceeds the eutectoid temperature ("800'C) while subsequent recrystallization in the primary a is accompanied by dissolution of Kiv particles dispersed in this constituent. The recrystallized a grains remain equiaxed and appear annealed despite large displacements onward into the resulting stir zone (SZ). Characteristic shear texture components are retained in the thermomechanically affected zone (TMAZ) but the texture of the primary a becomes random after recrystallization and remains so into both single-pass and multipass SZs. Mechanisms to account for recrystallization and subsequent deformation are proposed.Office of Naval ResearchNOOO I 409WR2020

The effect of concurrent straining on phase transformation in NiAl bronze during the friction stir processing thermomechanical cycle

The article of record as published may be found at http://dx.doi.org/10.1007/s11661-011-0638-7Equivalent strains up to a value of ⊨2.7 were determined by evaluation of the shape changes of the phases in a duplex a(fcc)/b(bcc) microstructure formed ahead of the pin tool extraction site during the friction stir processing (FSP) thermomechanical cycle in a cast NiAl bronze alloy. Correlation of the local strains with volume fractions of the various microstructure constituents in this alloy shows that the concurrent straining of FSP results in acceleration of the a + b fi b reaction in the thermomechanically affected zone (TMAZ) ahead of the pin extraction site. The resulting volume fraction of b (as determined by the volume fraction of its transformation products formed during post-FSP cooling) corresponds closely to the volume fraction expected for the peak stir zone temperature measured separately by means of thermocouples embedded within the tool pin profile along the tool path. The stir zone (SZ) in this material exhibits near-equilibrium microstructures despite brief dwells near the peak temperature (Tpeak ⊨ 0.95 Tmelt), reflecting large local strains and strain rates associated with this process.Defense Advanced Projects Agency (DARPA)Offoce of Naval ResearchContract no. N00014-06-WR-2-0196 (ONR)Contract no. N00014-09-WR20201 (ONR

Microstructural modification of as-cast NiAl bronze by friction stir processing

The application of friction stir processing (FSP) to a cast NiAl bronze (NAB) material is presented as a means for selective modification of the near-surface layers by converting as-cast microstructures to a wrought condition in the absence of macroscopic shape change. This may enable selective surface hardening of cast components. The complex physical metallurgy of the NAB is reviewed, and microstructure changes associated with FSP for a selected set of processing parameters are examined by optical microscopy (OM) and transmission electron microscopy (TEM) methods. Direct temperature measurement in the stir zone is infeasible and, so, these microstructure changes are used to estimate peak temperatures in the stir zone. The persistence of a Fe3Al phase (Kii) indicates that peak temperatures are below the solvus for this phase, while the presence of transformation products of the f3 phase, including fine Widmanstätten a., bainite, and martensite, indicates that peak temperatures exceed the eutectoid temperature for the reaction β →ᵅ + Kiii throughout the stir zone.Defense Advanced Research Projects Agency (DARPA