Role of microstructure on initiation and propagation of fatigue cracks in precipitate strengthened Cu–Ni–Si alloy (original) (raw)
Related papers
Characterization of uniaxial fatigue behavior of precipitate strengthened Cu-N.PDF
Fatigue tests were conducted on cylindrical bars specimens to understand the fatigue behavior of SICLANIC ® . Although it displays good resistance in monotonic tension, this material weakens and shows a softening in repeated solicitation. This has been verified through a SEM observation, the Cu-Ni-Si alloy presents transgranular failure by cleavage. The Manson-Coffin diagram exhibited the plastic deformation accommodation. The plastic deformation becomes periodic and decreases progressively as the cycle number increases. The approximations of Manson Coffin give fatigue parameters values which are in good agreement with the experience.
Low cycle fatigue behaviour of a precipitation hardened Cu-Ni-Si alloy
International Journal of Fatigue, 2016
Low cycle fatigue tests were performed at room temperature to investigate the role of the microstructure of a Cu-Ni-Si alloy on the stress response to strain cycling and on the fatigue resistance. The cyclic accommodation consisted in a hardening followed by a softening. TEM analysis showed that in some grains dislocations remained isolated and confined between precipitates while in other grains dislocations piled up at δ-Ni 2 Si precipitates and then cut them. Repetitive cutting allows their dissolution and formation of precipitate-free bands where the plastic deformation is localised. The Manson-Coffin diagram exhibited two regimes according to the proportion of grains involved in the plastic deformation accommodation. Keywords copper alloys-cyclic properties-low cycle fatiguemicrostructure-microscopy Highlights Investigated Cu-Ni-Si contains δ-Ni 2 Si nano precipitates-Cyclic hardening followed by softening is observed-Dissolution of δ-Ni 2 Si results from repetitive cutting-Deformation is localised in precipitate-free bands Highlights Investigated Cu-Ni-Si contains a high density of δ-Ni 2 Si precipitates-Cyclic hardening followed by softening is observed-Dissolution of δ-Ni 2 Si results from repetitive cuttinglocalisation of deformation in precipitate-free bands
Characterization of fatigue failed aged Cu-Ni-Si alloys
2018
The precipitation hardenable and non-toxic Cu-Ni-Si alloys are good alternatives to Cu-Be and Cu-Co-Ni-Be alloys due to their high strength and high conductivity that can be attained by not only alloying but also thermo-mechanical routes. In this study, the fractographic analysis was carried out to understand the fatigue failure of aged 2.55Ni-0.55Si0.25Zr-0.25Cr (wt-%) alloy which is a member of Corson family. In fatigue tests, a constant amplitude loading was applied at a stress ratio (R = σmin/σmax) of -1 and different stress levels (400, 350, 200 and 175 MPa) were used. The fracture response of the alloy was discussed depending on the applied stress levels and microstructural features. It was concluded that (i) Ni,Zr-rich precipitates and Cr-rich precipitates at the grain boundaries caused crack nucleation at all stress levels and (ii) the interaction between Ni-rich silicides and dislocations at lower stress level resulted in localized shearing and fine striations.
A microcalorimetric study of fatigue crack propagation in precipitation-hardened Cu-Co-Si alloys
Materials Letters, 1992
Measurements of fatigue crack propagation rates in Cu-0.67 at% Co-l. 1 at% Si and Cu-0.34 at% CoO .95 at% Si alloys have been made in order to investigate the influence of precipitation processes. The ageing treatment was found to decrease crack growth rates at lower values of the stress intensity factor. Microcalorimetric analysis of plastic zones revealed that precipitate destruction increases with the stress intensity amplitude according to a AK 'I2 law on the basis of a simple continuum mechanics model. The increase in precipitate destruction is associated with the enhanced tendency of the slip distribution to become finer. At high growth rates close to the rapid tensile fracture region, it is suggested that the overall destruction process is lowered owing to the fact that plastic deformation concentrates mainty in the dimple walls. Microvoid coalescence appears to be largely unaffected by the presence of the precipitates.
Microstructure and Precipitate's Characterization of the Cu-Ni-Si-P Alloy
Journal of Materials Engineering and Performance, 2016
Microstructure of the Cu-Ni-SiP alloy was investigated by transmission electron microscopy (TEM). The alloy had 551 MPa tensile strength, 226 HV hardness, and 36% IACS electrical conductivity after 80% cold rolling and aging at 450°C for 2 h. Under the same aging conditions, but without the cold rolling, the strength, hardness, and electrical conductivity were 379 MPa, 216 HV, and 32% IACS, respectively. The precipitates identified by TEM characterization were d-Ni 2 Si. Some semi-coherent spherical precipitates with a typical coffee bean contrast were found after aging for 48 h at 450°C. The average diameter of the observed semi-coherent precipitates is about 5 nm. The morphology of the fracture surface was observed by scanning electron microscopy. All samples showed typical ductile fracture. The addition of P refined the grain size and increased the nucleation rate of the precipitates. The precipitated phase coarsening was inhibited by the small additions of P. After aging, the Cu-Ni-SiP alloy can gain excellent mechanical properties with 804 MPa strength and 49% IACS conductivity. This study aimed to optimize processing conditions of the Cu-Ni-SiP alloys.
Microstructure and Fatigue Behavior of a Ni-Cu-Sn Alloy
Metals
In this paper, the static and fatigue properties of a Cu-Ni-Sn alloy are investigated. Tensile tests, hardness tests and microstructural analyses using optical and scanning electron microscopy (SEM) were performed and two sets of fatigue tests, with load ratio (R) R = − 1 and R = 0 , respectively, were carried out. The results showed the capability of the alloy to bear high static stress, thanks to its good strength properties. However, the fatigue tests showed a strong sensitivity of the alloy fatigue properties depending on the raw material batch. The comparison between microstructural analyses and fatigue test results showed a strong correlation; in particular, the specimens having a more inhomogeneous microstructure showed lower durability. In addition, the different microstructure also affected the fracture surface morphology as highlighted by SEM analyses.
Metallurgical Transactions A, 1987
The fatigue crack growth rates of four Alloy 718 microstructures comprising a two-by-two matrix of grain size and 3'" precipitate size were determined in air at 427 ~ and 0.33 Hz. For a stress ratio of 0.05, slower Region II rates were obtained for coarse-grained microstructures, independent of 3"" size, and microstructures with large 3'", independent of grain size. In the near-threshold regime, the coarse-grained microstructures again showed slower growth rates (higher AK,h), whereas the effect of 3'" size was mixed. Deformation modes were studied using scanning and transmission electron microscopy. Fatigue deformation resulted in the formation of slip bands which were longer for coarse-grained microstructures and typically spaced farther apart and more planar for large 3/' microstructures. The concepts of dislocation reversibility and slip band strain localization were used to explain the microstructural effects. Fatigue morphologies and cyclic constitutive behavior were consistent with the observed deformation modes. For a stress ratio of 0.75, the effects of grain size and 3'" size were essentially identical to those observed for a stress ratio of 0.05. This indicated that roughness-induced closure had a minimal influence on the differences that were observed in fatigue crack growth behavior.
SEM studies of fractures in spinodally hardened Cu-9Ni-6Sn-X alloys
In a recent study it was shown that hardening by a spinodal decomposition process in Cu-9Ni-6Sn can be controlled to some extent by quaternary trace element additions. The added trace element did not have any influence on the spinodal decomposition process, but it significantly influenced the kinetics of the formation of the (CuNi) Sn precipitate. Because of the beneficial hardening observed in these alloys, the Cu-Ni-Sn spinodal alloys have come into commercial prominence in recent years [4, 5]. In the light of this, it was considered worthwhile to examine the fracture behaviour of these alloys in different thermally treated conditions.
Twinning Induced Plasticity and Work Hardening Behavior of Aged Cu–Ni–Si Alloy
MATERIALS TRANSACTIONS, 2014
The work hardening behavior and deformed microstructure of the CuNiSi alloy aged at 723 K for various times and then deformed at 293 and 77 K were extensively investigated. The precipitate microstructure was also observed using transmission electron microscopy after aging treatment at 723 K for 0.30, 3.6, 64.8 and 345.6 ks. Deformation twins were clearly observed by transmission electron microscopy in the under-aged specimen deformed by 10% in tension at 293 K, in accordance with the enhanced work hardening rate observed during tensile deformation. The thickness of the deformation twins observed was approximately 140 nm. In addition, a significant fraction of larger deformation twins were observed by EBSD on the surface of the under-aged and peak-aged specimens tested at 77 K, for which the stressstrain behavior exhibited a nearly constant work hardening rate, i.e., high tensile strength and high elongation. These results show that the deformation twins formed during tensile deformation at 293 K contribute to strengthening of the specimen as new obstacles to the dislocation slip. Moreover, the enhanced twinning deformation at 77 K achieves high strength and elongation in the under-aged and peak-aged conditions. On the other hand, only a few deformation twins were observed in the supersaturated solid solution and over-aged specimens.
FATIGUE CRACK INITIATION AND GROWTH BEHAVIOR OF Cu‐16 at.% A1 SINGLE CRYSTALS
Fatigue & Fracture of Engineering Materials & Structures, 1991
In an attempt to understand the fatigue crack initiation and growth behavior of planar slip alloys, studies have been carried out in strain control on Cu‐16 at.% A1 single crystals oriented for easy glide. Alloy single crystals of Cu‐16 at.% A1 do not show saturation like copper crystals, but harden slowly and steadily throughout life, for the whole range of amplitudes applied. Cracks, the initiation and growth of which were studied by the sharp corner technique, were found to initiate when the peak stress reached 32 MPa irrespective of strain amplitude. The distribution of crack sizes in Cu‐16 at.% A1 single crystals was found to be more skewed to small cracks than that of copper. This behavior is attributed to the frequent migration of the bands of localized slip in this material. The fatigue lives of this alloy at low strain amplitudes (ypm < 6‐7 × 10−3) were found to be longer than those of copper single crystals because the strain is distributed more homogeneously than in co...