Performance of candidate gas turbine abradeable seal materials in high temperature combustion atmospheres

Abstract

AbstractThe development of abradeable gas turbine seals for higher temperature duties has been the target of an EU‐funded R&D project, ADSEALS, with the aim of moving towards seals that can withstand surface temperatures as high as ∼ 1100°C for periods of at least 24,000 h. The ADSEALS project has investigated the manufacturing and performance of a number of alternative materials for the traditional honeycomb seal design and novel alternative designs.This paper reports results from two series of exposure tests carried out to evaluate the oxidation performance of the seal structures in combustion gases and under thermal cycling conditions. These investigations formed one part of the evaluation of seal materials that has been carried out within the ADSEALS project.The first series of three tests, carried out for screening purposes, exposed candidate abradeable seal materials to a simulated natural gas combustion environment at temperatures within the range 1050–1150°C in controlled atmosphere furnaces for periods of up to ∼ 2,500 h with fifteen thermal cycles. The samples were thermally cycled to room temperature on a weekly basis to enable the progress of the degradation to be monitored by mass change and visual observation, as well as allowing samples to be exchanged at planned intervals. The honeycombs were manufactured from PM2000 and Haynes 214. The backing plates for the seal constructions were manufactured from Haynes 214. Some seals contained fillers or had been surface treated (e.g. aluminised).The second series of three tests were carried out in a natural gas fired ribbon furnace facility that allowed up to sixty samples of candidate seal structures (including honeycombs, hollow sphere structures and porous ceramics manufactured from an extended range of materials including Aluchrom YHf, PM2Hf, Haynes 230, IN738LC and MarM247) to be exposed simultaneously to a stream of hot combustion gas. In this case the samples were cooled on their rear faces to produce a temperature gradient through the seals and the samples were thermally cycled by switching the natural gas off every three hours. The total exposure period for each test was ∼ 1,000 h, with seal face temperatures of 1000–1180°C.The performance of the materials in these tests was evaluated using visual observations and cross‐sectional examinations using optical and SEM/EDX techniques. The data gathered have included measurements of oxide thickness and metal‐loss on the exposed samples.A wide range of materials performances has been observed in these studies from minimal damage through to total destruction of samples. Overall, this study has shown that there is still a lot of development work required in order to move to higher temperature sealing systems structures in gas turbine applications.