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

PRÉCIPITATION DANS LES JOINTS DE GRAINS.PRECIPITATION AT GRAIN BOUNDARIES

Les lois thermodynamiques de la précipitation intergranulaire ont été comprises qualitativement depuis 1951 [1] ; mais ce n'est qu'assez récemment que des tentatives fructueuses ont été faites pour quantifier ces réactions. Dans cet article, je me propose de faire le point sur l'état actuel des connaissances sur la précipitation intergranulaire et j'essaierai d'indiquer les problèmes qu'il faut résoudre à présent.The basic energetics of precipitation at grain boundaries has been qualitatively understood since 1951 [1] ; however, it is relatively recently that successful attempts have been made to quantify these reactions. In this article I intend to review the present state of knowledge of grain boundary precipitation and I will attempt to give an indication as to what problems have still to be solved

CRYSTALLOGRAPHY OF MARTENSITE IN A Cu-10Al-5Ni-5Fe ALLOY

The morphology and crystallography of quench-induced martensite in a Cu-10Al-5Ni-5Fe alloy has been studied using transmission electron microscopy. On quenching from 1000°C, the high temperature β-phase transformed to martensite based on the 3R-type structure. Numerous small iron-rich particles ~0.l µm diameter, were observed within martensite plates. The parallel-sided martensite plates were twin-related. When the alloy was quenched from the α+β phase field, the β-phase, which now had a higher aluminium content, transformed to martensite based on either the ordered 3R or 2H type structure. On tempering, the martensite phase rejected Ni, Al and Fe as precipitates based on NiAl and the matrix transformed to a f.c.c. copper-rich solid solution