Fatigue properties of B1914 superalloy at high temperatures

Vít Horník,Stanislava Fintová,Miroslav Šmíd,Pavel Hutař,Karel Hrbáček,Ludvík Kunz

doi:10.1016/j.prostr.2020.01.085

Abstract

B1914 is a nickel-based superalloy with an increased amount of B (boron) and C (carbon) to reach an adequate amount of borides and carbides in the cast structure ensuring improved creep properties. However, the influence of the structure on the material high-cycle fatigue properties is not sufficiently described. The present study brings the experimental results on the high-cycle fatigue properties of a cast polycrystalline nickel-based boron-rich B1914 superalloy, obtained at temperatures of 800, 900 and 950 °C. The cast superalloy was processed by hot isostatic pressing (HIP) to diminish the casting defects. The fatigue tests were performed in symmetrical loading in laboratory air. The fracture surfaces of the specimens were studied by scanning electron microscopy in order to describe the influence of temperature on the fatigue crack initiation and propagation. Change of the primary fatigue crack propagation mechanism from the crystallographic to the non-crystallographic mechanism was observed with increasing temperature. Decrease of a material lifetime and decrease of the fatigue endurance limit due to the increasing testing temperature was observed.

Highlights

Cast polycrystalline Ni-based superalloys are an advanced group of materials with good high-temperature strength and oxidation resistance
The polycrystalline MAR-M 247 superalloy investigated by Šmíd et al (2016) was processed by the hot isostatic pressing (HIP) treatment reducing the size of casting defects to the size of around 400 μm
The fatigue endurance limit of B1914 decreased to 190 MPa at 900 °C and it is lower than the fatigue endurance limit determined for MAR-M 247

Summary

Introduction

Cast polycrystalline Ni-based superalloys are an advanced group of materials with good high-temperature strength and oxidation resistance. These alloys are used in many high-temperature applications, e.g. energy or automotive industry. The superalloys components, for example, turbine blades and turbochargers wheels, are exposed to high-cycle fatigue loading due to high-frequency vibrations and creep loading due to centrifugal force during operation, e.g. The problem of cast materials is casting defects created during the manufacturing process. The casting defects act as stress concentrators, strongly predetermining material fatigue properties, e.g. Kunz et al (2012). The hot isostatic pressing (HIP) procedure is usually adopted to reduce the casting defects size and to improve fatigue properties as a result

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