Influence of shot peening on high-temperature corrosion and corrosion-fatigue of nickel based superalloy 720Li

Abstract

1High-temperature corrosion fatigue, a combination of corrosion with a fatigue cycle, is an emerging generic issue affecting power generation and aero gas turbine engines and has the potential to limit component life. Historically, surface treatments, such as shot peening have been used to improve component life and have been optimised for fatigue response. Research into optimisation of shot peening techniques for hot corrosion and high-temperature corrosion fatigue has shown 6-8A 230H 200% coverage to provide overall optimum performance for nickel-based superalloy 720Li based on the limited data within this study. Utilisation of electron backscatter diffraction techniques, in combination with detailed assessment of corrosion products have been undertaken as part of this work. The resultant cold-work visualisation technique provides a novel method of determining the variation in material properties due to the shot peening process and the interaction with hot corrosion. Through this work it has been shown that all three shot peening outputs must be considered to minimise the effect of corrosion fatigue, the cold work, residual stress and surface roughness. Further opportunity for optimisation has also been identified based on this work.

Factors affecting the corrosion fatigue life in nickel based superalloys for disc applications

“…Whilst this work was performed utilizing prepitted specimens, so that the exact mechanisms of cracking were not investigated, it provided insight into the peening process itself and demonstrated that residual stress was not the dominant feature but the resulting deformed grains at the surface of the material that prevents cracking. This has subsequently been confirmed [7] whereby it was shown that by optimisation of this layer, it is possible to delay cracking under conditions of both corrosion and fatigue.…”

“…Evidence suggests that time independent processes are required to provide regular disturbances to the developing oxide that allows diffusion of sulphur to the base metal. Oxide film rupture mechanisms have been shown previously [7] to affect the fatigue performance of materials under corrosive conditions. In this case temperatures were insufficient to induce creep, however it was shown that the inclusion of dwell and rate of stressing, 03001-p.5 MATEC Web of Conferences greatly affected life and under certain conditions life was extended beyond that in air.…”

Effect of Surface Mechanical Treatments on the Microstructure-Property-Performance of Engineering Alloys

“…Shot peening has been demonstrated as a fatigue life improvement process as reported by several researchers for steel [8,162,163,164,165,166], aluminum [9,11,14,167,168,169,170,171], magnesium [7,172], nickel [97,147,173,174,175], and titanium alloys [176,177,178,179,180,181,182,183,184,185,186,187,188] and as summarized or quantified in Table 1.…”

Análise Do Alívio Térmico De Tensões Residuais Do Aço Sae 4140 Por Difração De Raios-X Fast in-Situ

“…Observa-se que a mudança mais significativa na distribuição das T R ocorre na região superficial da estrutura tratada [12]. Medições in-situ já foram empregadas com sucesso por diversos pesquisadores para investigar propriedades de materiais [13], tais como transformações de fases [14], análise de fases [15] e T R [16], através de estudos analíticos, experimentais e computacionais [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][22][23][24][25]. Uma pesquisa cuja análise foi relacionada à relaxação das T R C induzidas por SP e a redistribuição, durante ensaios em regime de flexão rotativa de alto e de baixo ciclos em aço carbono (0,45%C 16.…”

“…Devido à condição de equilíbrio mecânico, essas T R C são balanceadas pela tensão residual trativa (T R T) em todo o volume do material [1]. Os efeitos benéficos do SP incluem o incremento da vida em fadiga (retardando a nucleação de trincas de fadiga) [1,2] e o aumento da resistência à corrosão [2]. Em contraponto, há o efeito deletério das T R C relaxarem em serviço, na presença de certos elementos cruciais e cotidianos, tais como: alta temperatura (T), cargas mecânicas (cíclicas ou não) / térmicas ou termomecânicas [3].…”