Abstract. An accelerated creep test was implemented to study the effects of heat treatment on the creep properties of INCONEL 617. Three heat treatment conditions were set on the test specimens, including 1) as-received, 2) aged as the simulation of service conditions at 650°C for 1,000 h and 3) solutionised. The accelerated creep test was performed at 700, 750, 800 and 900°C with applied stress at 80% and 90% of the yield stress (YS) at tested temperatures. The results were analysed for both time to rupture and % RA, which showed that there was a significant drop in time to rupture and % RA at 750°C. Subsequently, the % RA increased while the time to rupture gradually decreased. The Larson Miller curve for all heat treatment conditions could be plotted with an interest in the presence of an intersection zone. This indicated the possibility of failure behaviour changes from a creep mode to an overload mode at low applied loads to high applied loads, respectively.
In-situ observation of martensite decomposition at Heat Affected Zone (HAZ) was investigated on a dissimilar joining between 2.25Cr-0.5Mo grade T22 as base material and ER90S-B9 as filler metal using GTAW process using LEEM at a synchrotron facility. A post weld heat treatment (PWHT) cycle was simulated on a welded specimen in high vacuum chamber by heating cartridge and electron bombardment. Both effects PWHT duration and weld areas were studied for comparisons. At the simulated PWHT between 690°C -700°C in CGHAZ, martensite started to decompose by the dissolution of carbide flakes. The prior-austenite grain boundaries were also shown during the process. The same phenomena were also observed in FGHAZ with different extent. In un-affected base material, ferrite and new pearlite grains presented and grew at the expense of old pearlite. Longer PWHT duration resulted in more ferrite formed in all weld areas. Raising PWHT temperature to 730°C could push the reaction above Eutectoid temperature as the new austenite formed at grain boundaries. The proposed mechanism for martensite decomposition would be in steps as dissolution of carbide followed by formation of ferrite and growth as PWHT proceeded.
In this research, the Synchrotron X-ray lithography (X-ray LIGA) was implemented to fabricate imitative Stress Corrosion Crack (SCC) for using as a reference specimen of electromagnetic NDT. A pattern of the imitative SCC was created by using X-ray LIGA with controllable shape and size in precise details. The pattern created had a high aspect ratio, which was formed on SU-8 polymer. As a preliminary experiment, the prepared pattern was inserted into a block of pure Nickel formed by an electroplating technique. To develop a reference comparable to stainless steel in terms of electromagnetic response, the technique called “Suspension Electroplating” was implemented to create a block of material from its powder form. A rough magnetic response was then measured by Eddy Current Testing (ECT). The results showed the possibility of creating the desired properties of stainless steel. The SCC pattern will be then inserted to become the reference specimen.
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