Grain Boundary Strengthening Mechanism of Tungsten Containing 9 to 12% Chromium Ferritic Heat Resistant Steels at 650.DEG.C.

ABSTRACTThe creep behavior of a new type of austenitic heat-resistant steel Fe-20Cr-30Ni-2Nb (at.%), strengthened by intermetallic Fe2Nb Laves phase, has been examined. Particular attention has been given to the role of grain boundary Laves phase in the strengthening mechanism during long-term creep. The creep resistance increases with increasing area fraction (ρ) of grain boundary Laves phase according to equation ε/ε = (1−ρ), where ε0 is the creep rate at ρ = 0. In addition, the creep rupture life is also extended with increasing ρ without ductility loss, which can yield up to 77% of elongation even at ρ = 89%. Microstructure analysis revealed local deformation and well-developed subgrains formation near the grain boundary free from precipitates, while dislocation pile-ups were observed near the grain boundary Laves phase. Thus, the grain boundary Laves phase is effective in suppressing the local deformation by preventing dislocation motion, and thereby increases the long-term creep rupture strength. This novel creep strengthening mechanism was proposed as “grain boundary precipitation strengthening mechanism” (GBPS).

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Microstructure and Enhanced Properties of Copper-Vanadium Nanocomposites Obtained by Powder Metallurgy

Materials ◽

10.3390/ma12030339 ◽

2019 ◽

Vol 12 (3) ◽

pp. 339 ◽

Cited By ~ 1

Author(s):

Yong Wang ◽

Jinguo Wang ◽

Haohao Zou ◽

Yutong Wang ◽

Xu Ran

Keyword(s):

Electrical Conductivity ◽

Grain Size ◽

Yield Strength ◽

Grain Boundary ◽

High Strength ◽

Strengthening Mechanism ◽

Copper Matrix ◽

Dispersion Strengthening ◽

Annealed Copper ◽

Grain Boundary Strengthening

Cu-2.4 wt.%V nanocomposite has been prepared by mechanical alloy and vacuum hot-pressed sintering technology. The composites were sintered at 800 °C, 850 °C, 900 °C, and 950 °C respectively. The microstructure and properties of composites were investigated. The results show that the Cu-2.4 wt.%V composite presents high strength and high electrical conductivity. The composite sintered at 900 °C has a microhardness of 205 HV, a yield strength of 404.41 MPa, and an electrical conductivity of 79.5% International Annealed Copper Standard (IACS); the microhardness and yield strength reduce gradually with the increasing consolidation temperature, which is mainly due to the growth of copper grain size. After sintering, copper grain size and V nanoparticle both maintain in nanoscale; the strengthening mechanism is related to grain boundary strengthening and dispersion strengthening, while the grain boundary strengthening mechanism plays the most important role. This study indicates that the addition of small amounts of V element could enhance the copper matrix markedly with the little sacrifice of electrical conductivity.

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Creep Strengthening Mechanism of Mo and W in 9% Cr Heat Resistant Steels

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.171-174.499 ◽

1999 ◽

Vol 171-174 ◽

pp. 499-504 ◽

Cited By ~ 9

Author(s):

T. Muraki ◽

Yuki Hasegawa ◽

M. Ohgami

Keyword(s):

Strengthening Mechanism ◽

Heat Resistant ◽

Heat Resistant Steels

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Design and Synthesis of C-O Grain Boundary Strengthening of Al Composites

Nanomaterials ◽

10.3390/nano10030438 ◽

2020 ◽

Vol 10 (3) ◽

pp. 438

Author(s):

Jianian Hu ◽

Jian Zhang ◽

Guoqiang Luo ◽

Yi Sun ◽

Qiang Shen ◽

...

Keyword(s):

Tensile Strength ◽

Ultimate Tensile Strength ◽

Yield Strength ◽

Grain Boundary ◽

Pure Aluminum ◽

Polyvinyl Butyral ◽

Strengthening Mechanism ◽

Vertical Tube ◽

Al Matrix ◽

Grain Boundary Strengthening

This research presents an approach for C-O grain boundary strengthening of Al composites that used an in situ method to synthesize a C-O shell on Al powder particles in a vertical tube furnace. The C-O reinforced Al matrix composites (C-O/Al composites) were fabricated by a new powder metallurgy (PM) method associated with the hot pressing technique. The data indicates that Al4C3 was distributed within the Al matrix and an O-Al solution was distributed in the grain boundaries in the strengthened structure. The formation mechanism of this structure was explained by a combination of TEM observations and molecular dynamic simulation results. The yield strength and ultimate tensile strength of the C-O/Al composites, modified by 3 wt.% polyvinyl butyral, reached 232.2 MPa and 304.82 MPa, respectively; compared to the yield strength and ultimate tensile strength of the pure aluminum processed under the same conditions, there was an increase of 124% and 99.3%, respectively. These results indicate the excellent properties of the C-O/Al-strengthened structure. In addition, the strengthening mechanism was explained by the Hall–Petch strengthening, dislocation strengthening, and solid solution strengthening mechanisms, which represented contributions of nearly 44.9%, 15.9%, and 16.6% to the total increased strength, respectively. The remaining increment was attributed to the coupled strengthening of the C and O, which contributed 20.6% to the total increase.

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Correlation between Microstructure and Nanohardness in Advanced Heat-Resistant Steel

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.326-328.277 ◽

2006 ◽

Vol 326-328 ◽

pp. 277-280

Author(s):

Jae Il Jang ◽

Sang Hoon Shim ◽

Shinichi Komazaki ◽

Takayuki Sugimoto

Keyword(s):

Prior Austenite ◽

Complex Structure ◽

Strengthening Mechanism ◽

Resistant Steel ◽

Heat Resistant Steel ◽

Heat Resistant ◽

Austenite Grain ◽

Heat Resistant Steels ◽

Prior Austenite Grain

As advanced ferritic/martensitic heat-resistant steels generally have a complex structure consisting of several microstructural units (lath, block, packet, and prior austenite grain), it is very hard to separate the contribution of each microstructural unit (or its each boundary) to the strengthening mechanism in such steels. Here we explore the role of each microstructural unit in strengthening of advanced high Cr steel through nanoindentation experiments performed at different load levels. Nanoindentation results are analyzed by comparing with microstructural observations and discussed in terms of prevailing descriptions of strengthening mechanism.

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Mechanism of Gradient Strengthening Layer Formation Based on Microstructure and Microhardness of Inconel 718 Grinding Surface

10.21203/rs.3.rs-706030/v1 ◽

2021 ◽

Author(s):

Zhigang Dong ◽

Nianwei Xu ◽

Yuan Zhang ◽

Lu Han ◽

Renke Kang ◽

...

Keyword(s):

Grain Boundary ◽

Grain Refinement ◽

Inconel 718 ◽

Strengthening Mechanism ◽

High Density ◽

Microstructure Observation ◽

Dislocation Strengthening ◽

The Difference ◽

Dislocation Layer ◽

Grain Boundary Strengthening

Abstract Gradient strengthening layer will emerge on the grinding surface of Inconel 718 due to the difference of microstructure. The surface microstructure and microhardness are not independent of each other, and the microhardness is the embodiment of the microstructure evolution in the strength aspect. In this paper, the microstructure observation, microhardness experiments and strengthening theory were combined to analyze. The experimental results show that the grinding surface consists of grain refinement layer and high-density dislocation layer. The grain refinement layer is constituted of equiaxed nano-grains and elongated grains, in which grain boundary strengthening occurred leading to an increase in microhardness. Dislocation strengthening occurred in the high-density dislocation layer, in which the increment of dislocation density is approximately 3.54 × 109 mm− 2 compared with inner matrix. Microhardness of high-density dislocation region reaches the maximum (438.6 ± 11.1 HV0.01) because of the dislocation strengthening. The variation of microhardness is discussed from two strengthening mechanisms of grain boundary strengthening and dislocation strengthening, and the strengthening mechanism in the different regions of grinding surface is revealed. The calculated microhardness increments through these mechanisms in the refined-grain region and the high-density dislocation region are basically consistent with the measured values.

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Grain Boundary Character of 9Cr Feritic/Martensitic Heat Resistant Steels Strengthened by Nano-Sized MX Precipitates

Materials Science Forum ◽

10.4028/www.scientific.net/msf.638-642.2882 ◽

2010 ◽

Vol 638-642 ◽

pp. 2882-2887

Author(s):

Feng Shi Yin

Keyword(s):

Grain Boundary ◽

Electron Backscatter Diffraction ◽

Stress Rupture ◽

Low Carbon ◽

Boundary Character ◽

Carbon And Nitrogen ◽

Heat Resistant ◽

Grain Boundary Character ◽

Nitrogen Contents ◽

Heat Resistant Steels

In this work, two heats of 9Cr ferritic/martensitic heat resistant steels with different carbon and nitrogen contents were prepared. The steels were designed to have much lower carbon content than conventional 9-12Cr heat resistant steels for obtaining dense nano-sized MX precipitates. Microstructure of the two steels in different heat treatment states was analyzed by electron backscatter diffraction (EBSD) method. The results show that grain boundary character is greatly affected by carbon and nitrogen contents. Martensite in the steel with 0.02wt.% carbon and ultra low nitrogen is easier to recrystallize than that in the steel with ultra low carbon and 0.03wt.% nitrogen during tempering treatment. The effect of grain boundary character on stress rupture properties is also discussed.

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Study on Strengthening Mechanism of 9Cr-1.5Mo-1Co and 9Cr-3W-3Co Heat Resistant Steels

Materials ◽

10.3390/ma13194340 ◽

2020 ◽

Vol 13 (19) ◽

pp. 4340 ◽

Cited By ~ 1

Author(s):

Long Zhao ◽

Xiangru Chen ◽

Tieming Wu ◽

Qijie Zhai

Keyword(s):

Strengthening Mechanism ◽

Microstructure Analysis ◽

Resistant Steel ◽

Heat Resistant Steel ◽

Steel Microstructure ◽

Heat Resistant ◽

High Temperature Mechanical Properties ◽

The Matrix ◽

Solution Strengthening ◽

Heat Resistant Steels

The strengthening mechanism of 9Cr–1.5Mo–1Co and 9Cr–3W–3Co heat resistant steel was studied by tensile test and microstructure analysis. At the same temperature, the yield strength of 9Cr–3W–3Co heat-resistant steel is higher than that of 9Cr–1.5Mo–1Co heat-resistant steel. Microstructure analysis proved that the strength of 9Cr–1.5Mo–1Co and 9Cr–3W–3Co heat-resistant steel is affected by grain boundary, dislocation, precipitation, and solid solution atoms. The excellent high temperature mechanical properties of 9Cr–3W–3Co heat-resistant steel are mainly due to the solution strengthening caused by Co and W atoms and the high-density dislocations distributed in the matrix; however, 9Cr–1.5Mo–1Co heat-resistant steel is mainly due to the martensitic lath and precipitation strengthening.

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