Dependence of mechanical strength on grain structure in the<i>γ</i>' and oxide dispersion-strengthened nickelbase superalloy PM 3030

Nganbe, Michel; Heilmaier, Martin; Schultz, L.

doi:10.3139/146.101080

Cited by 5 publications

(8 citation statements)

References 18 publications

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“…One sample was tested for each test temperature; the results are shown in Figure 3. It should be pointed out that overall strength level and temperature dependence for PM 3030 materials are known from previous studies [12,13] . The tests performed on R50 merely helped to assess the relative strength different caused by the different recrystallization defect volume fractions.…”

Section: Impact Of Recrystallization Defects On Materials Strength As mentioning

confidence: 98%

“…This decrease can be explained by stronger diffusion and grain boundary deformation processes in recrystallization defect areas [17,18] . In the equicohesion temperature range around 650-680 8C [12,13,19] , no effect of recrystallization defects was expected because grain boundary and grain interior are supposed to have equal strength in this range. The observed relatively broad equicohesion range in contrast to a precise single equicohesion temperature may be due to slight differences in hardening particle parameters.…”

Section: Impact Of Recrystallization Defects On Materials Strength As mentioning

confidence: 99%

“…Trend lines are plotted based on knowledge of overall stress level and temperature dependence from previous publications. [12,13] The equicohesion temperature range is also shown (hatched). This plateau strength is maintained until 100 vol% recrystallization defects, which corresponds to a completely fine grain material.…”

Section: Effect Of Recrystallization Defect Volume Fraction and Grainmentioning

confidence: 99%

“…This plateau strength is maintained until 100 vol% recrystallization defects, which corresponds to a completely fine grain material. The initial logarithmic fall in strength obeys the following empirical equations for YS and UCS, respectively [13] :…”

Section: Effect Of Recrystallization Defect Volume Fraction and Grainmentioning

confidence: 99%

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Impact of Recrystallization Defects on the High Temperature Strength of PM 3030

Nganbe

2009

Adv Eng Mater

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The advantage of single crystals has been established for materials used at high temperatures. They are usually manufactured by directional solidification using a premanufactured seed crystal; however, the production of single crystals cannot only be relatively costly, but can even be impossible for some ceramic particle strengthened materials. Homogeneously incorporating thermally stable ceramic dispersoids in a metal melt is very difficult due to strong differences in densities between the two phases. Therefore, such materials are usually manufactured by powder metallurgy (PM), which generally produces ceramic dispersion strengthened alloys initially with an isotropic and fine grain structure. It is then necessary to complete a secondary recrystallization [1,2] of the initial PM material in order to achieve a coarse and elongated grain structure that has proven to show high temperature strength properties close to those of single crystals. [3,4] It should be pointed out that secondary recrystallizing such materials into a single crystal structure is generally too costly or even impossible due to pinning of grain boundaries at hardening particles or segregation of dispersoids. Furthermore, it is well known that not all grains grow into a coarse and elongated structure during secondary recrystallization. Rather, pockets of nonrecrystallized fine grains usually remain, which are then called recrystallization defects. Although the latter are readily recognized as preferred locations for initiation of high temperature damage and failure in ODS superalloys, [5,6] their effect on the actual deformation resistance and high temperature strength has barely been investigated. The present work closes this gap by assessing and quantifying the influence of recrystallization defects on the strength of an oxide dispersion and g 0 precipitation strengthened nickel base superalloy, PM 3030. It shows the dependence of this influence on temperature, recrystallization defect volume fraction, and grain size. The developed principle understanding can be very useful for economically achieving optimal properties. In fact, while completely eliminating recrysallization defects can be imperative for some critical applications, setting their maximal tolerated content too low can lead to unnecessary challenges for process control and excessive manufacturing costs for less critical applications. Materials and Their ManufactureAn incompletely secondary recrystallized batch of PM 3030, a Ni-base superalloy manufactured by Plansee GmbH (Lechbruck, Germany), was investigated. The material was manufactured by the PM route. [7,8] Mechanical alloying (MA) [9,10] of prealloyed powders produced a homogeneous alloy containing a fine oxide dispersion; the nominal chemical composition of PM 3030 is 17Cr-2Mo-3.5W-2Ta-6.6Al-1.1Y 2 O 3 -bal. nickel. The mechanically alloyed powders were then compacted using hot isostatic pressing (HIP) and underwent a company specific thermomechanical treatment including hot extrusion to a final round bar with a diameter o...

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Section: Impact Of Recrystallization Defects On Materials Strength As mentioning

confidence: 98%

Section: Impact Of Recrystallization Defects On Materials Strength As mentioning

confidence: 99%

Section: Effect Of Recrystallization Defect Volume Fraction and Grainmentioning

confidence: 99%

Section: Effect Of Recrystallization Defect Volume Fraction and Grainmentioning

confidence: 99%

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Impact of Recrystallization Defects on the High Temperature Strength of PM 3030

Nganbe

2009

Adv Eng Mater

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“…k is a fit constant and is determined to be 9 for both R90 and R901315; it is obvious that the value of k is expected to vary with material and test conditions such as strain rate. T Equi is the equicohesion temperature and was determined in previous publications (Ref 11,18) to be around 700°C for PM 3030; and T is the absolute temperature in Kelvin. The dependence of a on temperature is plotted in Fig.…”

Section: Exponential Drop Of the Grain Boundary Strengthening Coefficmentioning

confidence: 99%

Equicohesion: Intermediate Temperature Transition of the Grain Size Effect in the Nickel-Base Superalloy PM 3030

Nganbe

Fahim

2009

J. of Materi Eng and Perform

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The intermediate temperature transition of the grain size effect on the yield strength of PM 3030 is investigated using compression tests from room temperature to 1200°C. It is found that grain boundary strengthening is strong at low temperature which is consistent with conventional Hall-Petch hardening. However, the grain boundary contribution to strength diminishes exponentially at intermediate temperature and vanishes at the equicohesion point. Above the equicohesion point, finer grain structure leads to material softening primarily due to grain boundary diffusion and deformation processes. Maximum softening occurs at T soft-max which is about 70% of the melting point, then decreases logarithmically with further increase in temperature, and vanishes at the melting point. This can well be rationalized by the overwhelming dominance of volume diffusion over grain boundary diffusion at temperatures close to the melting point, which decreases the impact of grain size on material strength. An exponential transition from the Hall-Petch behavior to the diffusion-based behavior provides an overall better fit of test data as compared to a linear transition. This study provides a contribution to the understanding of equicohesion and variation of the grain size effect on material strength and can be particularly crucial for components used at intermediate temperature.

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Microstructure and mechanical properties of γ΄ strengthened Co–Ni–Al–W-base ODS alloys

Zhang

Qin

et al. 2012

Materials Chemistry and Physics

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Dependence of mechanical strength on grain structure in theγ' and oxide dispersion-strengthened nickelbase superalloy PM 3030

Cited by 5 publications

References 18 publications

Impact of Recrystallization Defects on the High Temperature Strength of PM 3030

Impact of Recrystallization Defects on the High Temperature Strength of PM 3030

Equicohesion: Intermediate Temperature Transition of the Grain Size Effect in the Nickel-Base Superalloy PM 3030

Microstructure and mechanical properties of γ΄ strengthened Co–Ni–Al–W-base ODS alloys

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