Effects of Hot Repressing on Fatigue Behaviour of Powder Metallurgy, Normalized Fe–O·3C Steels

Hardmetals, manufactured from powders by pressing and sintering, are the most important tool materials in service today. In many applications, such as milling or percussion drilling, they are subjected to fatigue with considerable loading cycle numbers. In the present study, the fatigue behaviour of hardmetals in push-pull loading was investigated up to Nmax= 1010using ultrasonic resonance fatigue testing. It showed that with all hardmetal grades investigated there is no fatigue “limit”, i.e. a horizontal branch of the S-N curve, but a consistent drop of the curve up to maximum N. Crack initiation was found to occur predominantly microstructure-controlled, as compared to defect controlled as typical for powder metallurgy tool steels.Keywords: gigacycle fatigue, WC-Co hardmetals, ultrasonic fatigue testing, fatigue limit

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Fatigue Behaviour and Crack Initiation in CoCrFeNiMn High-Entropy Alloy Processed by Powder Metallurgy

Metals ◽

10.3390/met9101110 ◽

2019 ◽

Vol 9 (10) ◽

pp. 1110 ◽

Cited By ~ 5

Author(s):

Zdeněk Chlup ◽

Stanislava Fintová ◽

Hynek Hadraba ◽

Ivo Kuběna ◽

Monika Vilémová ◽

...

Keyword(s):

Powder Metallurgy ◽

Cyclic Loading ◽

Crack Nucleation ◽

Milled Powder ◽

Fatigue Behaviour ◽

Initiation Site ◽

High Entropy Alloy ◽

High Entropy ◽

Fine Grained ◽

Small Change

Single-phase equiatomic five-element high entropy alloy CoCrFeMnNi was prepared by powder metallurgy. Two materials with ultra-fine-grained microstructure were prepared by spark plasma sintering (SPS) of ball-milled powder at two sintering times (5 and 10 min), assigned as HEA 5 and HEA 10, respectively. Basic microstructural and mechanical properties were evaluated. The median grain size of the microstructures was determined to be 0.4 and 0.6 μm for HEA 5 and HEA 10, respectively. The differences in the microstructure led to a significant change in strength and deformation characteristics evaluated at room temperature. The effect of cyclic loading was monitored by three-point bending fatigue test. The results show that even relatively small change in the microstructure causes a significant effect on fatigue life. The fatigue endurance limit was measured to be 1100 MPa and 1000 MPa for HEA 5 and HEA 10, respectively. The detailed fractographic analysis revealed that abnormally large grains, localised in the microstructure on the tensile loaded surface, were a typical fatigue initiation site. The formation of (nano) twins together with dislocation slips caused the crack nucleation because of the cyclic loading.

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Thermomechanically processed powder metallurgy Ti-5Fe alloy: effect of microstructure, texture, Fe partitioning and residual porosity on tensile and fatigue behaviour

Materialia ◽

10.1016/j.mtla.2021.101254 ◽

2021 ◽

pp. 101254

Author(s):

Carlos Romero ◽

Fei Yang ◽

Stella Raynova ◽

Leandro Bolzoni

Keyword(s):

Powder Metallurgy ◽

Fatigue Behaviour ◽

Residual Porosity ◽

Alloy Effect ◽

Effect Of Microstructure

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An Investigation of Fracture Origins in Heat-Treated Ti49Al47Cr2Nb2 Powder Compacts

Materials Science Forum ◽

10.4028/www.scientific.net/msf.638-642.1422 ◽

2010 ◽

Vol 638-642 ◽

pp. 1422-1427

Author(s):

Olivier Berteaux ◽

Roger Valle ◽

Monique Raffestin ◽

Marc Thomas ◽

G. Henaff

Keyword(s):

Powder Metallurgy ◽

Crack Initiation ◽

Fatigue Behaviour ◽

Structural Defects ◽

Treatment Conditions ◽

Heat Treated ◽

Initiation And Propagation ◽

Metallic Inclusions ◽

Defect Sensitivity ◽

Powder Compacts

The fatigue behaviour of a powder-metallurgy (PM) + heat-treated Ti49Al47Cr2Nb2 alloy is investigated using detailed SEM characterization. Based on the results of comparative static and cyclic loadings at RT, the fracture origins for the different test specimens is investigated. Conventional fractographic analyses revealed that internal structural defects inherent to powder metallurgy such as compaction defects, porosities and non-metallic inclusions can promote crack initiation. However, the fracture surface of test specimens is markedly affected by the microstructure, which is indicative of the microstructure dependence on crack initiation and propagation. In sub-transus heat treatment conditions, the detrimental effect of structural defects is illustrated by clear crack initiation sites onto the fracture surfaces. In super-transus conditions, crack propagation from defects can be blunted due to crack deflection, branching through lamellar interfaces, thus leading to lower defect sensitivity. Correlation of the results of these microfractographic examinations with the stress-strain curves corresponding to the various specimens allows identifying the role of such structural defects on the static and cyclic deformation behaviours. Finally, implications of such dependencies will be assessed relative to the requirements for aerospace gas turbine applications.

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