Session: 03-06 Metals: Mechanical Properties

Paper Number: 91410

91410 - Effect of Short Cycle Heat Treatments on Microstructure and Mechanical Properties of Additively Manufactured Mar-M 509 

Co based superalloy Mar-M 509 shows excellent resistance towards hot corrosion and oxidation which make it suitable for static and durable components such as nozzle guiding vanes in aircraft engines and in ground-based gas turbines. It is primarily strengthened by carbide precipitation hardening and solid solution strengthening mechanism. With the growth of additive manufacturing as an end-use manufacturing process, Mar-M 509 can also prove to be a candid material for thermal liners with internal cooling structures. However, it’s low ductility at ambient and elevated temperature (beyond 850 ℃) could possibly lead to cracking under thermal cycling and limit its utility in rotary components. The present study deals with the influence of microstructure on mechanical properties of Mar-M 509 fabricated using laser based- powder bed fusion (PBF-LB) system in the as-printed and heat-treated conditions. Initially, material characterization techniques were used to rationalize the pre-alloyed powder and as-built superalloy behaviour. Two different geometries, i.e., cuboid and cylinder are fabricated and, both longitudinal and transverse planes are investigated. Peaks corresponding to FCC phase are confirmed through XRD analysis. Residual stresses are estimated by comparison to the powder pattern. Porosity fraction is characterized using Archimedes route as well as cross-section imaging using optical and scanning electron microscopy. Scanning electron microscopy showed elongated columnar structure with carbide precipitation in the inter-dendritic region. The as-printed alloy showed improved mechanical properties relative to the as-casted Mar-M509 [1,2]. In the as printed state the transverse orientation showed 20% higher Yield Strength (YS) and 5% higher Ultimate Tensile Strength (UTS) relative to longitudinal orientation, which is a result of the microstructural anisotropy expected in PBF technique. The fracture surface of micro-tensile samples showed cleavage facets with columnar dendrite pattern in both orientations. Short-cycle heat treatments were designed to study the interplay of carbide precipitates with mechanical properties. Conventional heat treatment includes a two-step process, solutionising at 1260⁰C for 4hrs followed by ageing at 850⁰C for 24hrs which did not yield in significant improvement in mechanical properties [3] and is also energy intensive. Short term heat treatments were conducted at 950, 1050, and 1150,  , for 1 and 3 hrs and later their microstructure and mechanical properties were characterised. These results are used to discuss the root cause of low ductility at room temperature in Mar-M509 superalloy and the significance of rapid heat treatment cycles for optimizing the microstructure to improve the performance of the superalloy.

Keywords- Mar-M509, Powder Bed Fusion-Laser Based (PBF-LB), Mechanical properties, Microstructural anisotropy.

Presenting Author: Shreehard Sahu Indian Institute of Technology, Bombay

Presenting Author Biography: Shreehard Sahu is working as Project Technical Researcher at Indian Institute of Technology, Bombay. He was awarded the K.K. Malik medal for being "best master's student" at Indian Institute of Science, Bengaluru. His primary research interest is understanding structural failure in metallic materials. He also looks into metallurgical phenomena in manufacturing process such as welding, additive manufacturing and thermal spray coatings.

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