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Properties and applications of engineering materials
Published in Alan Darbyshire, Charles Gibson, Mechanical Engineering, 2023
Alan Darbyshire, Charles Gibson
The precipitation process can be speeded up by re-heating the material to between 120°C and 160°C for a period of around 10 h. The final hardness and strength is then greater than that achieved by age hardening at room temperature. Aluminium alloys which contain silicon and magnesium also respond to precipitation hardening. Here it is the intermetallic compound Mg2Si which precipitates. See Table 5.8 for aluminium alloys which can be heat treated.
Types of Corrosion in the Offshore Environment
Published in Karan Sotoodeh, Coating Application for Piping, Valves and Actuators in Offshore Oil and Gas Industry, 2023
The other material vulnerable to pitting corrosion in the offshore environment is 17-4PH stainless steel. “PH” in front of the material name stands for precipitation hardening heat treatment process. The high strength of 17-4PH comes from its heat treatment. Precipitation hardening, also called age hardening, is a process in which the hardness and mechanical strength of a material are enhanced significantly by the formation of extremely small, uniformly distributed particles of a second phase within the original phase matrix, in this case, copper participation. 17-4PH is a very hard martensitic stainless steel containing about 17% chromium, 4% nickel and 4% copper. It is selected in onshore plants, like petrochemical plants and refineries, for valve stems or shafts due to its high strength. However, 17-4PH is at high risk of pitting and SCC in chloride-containing environments. Figure 1.25 illustrates pitting and SCC on a 17-4PH shaft in the offshore sector caused by contact with chloride. Thus, it is not recommended to select 17-4PH for valve shafts in the offshore environment. The alternative shaft or stem material in offshore is Inconel 718. Inconel 718, like 17-4PH, is a very strong and hard material that has undergone age-hardening heat treatment. CLSCC is explained in the next subchapter of this section.
Challenges and Common Strategies
Published in Mirco Peron, Filippo Berto, Jan Torgersen, Magnesium and Its Alloys as Implant Materials, 2020
Mirco Peron, Filippo Berto, Jan Torgersen
Precipitation hardening is one of the methods used to improve the mechanical properties of a metal. The precipitation hardening mechanism helps in increasing the difficulty of movement for dislocations due to appropriate distribution of particles at the grain boundaries and inside the grains. It is preferable to obtain a homogeneous distribution of particles, since a nonhomogeneous concentration of the precipitates leads to nonhomogeneous mechanical properties. The size of the particles is very important: small size particles give better mechanical properties. The hardening effect is due both to an increase in the difficulty of the dislocation motion and to an increase in the concentration of dislocations through a mechanism known as Orowan looping [31].
Influence of various trace metallic additions and reinforcements on A319 and A356 alloys—a review
Published in Cogent Engineering, 2022
D Srinivas, Gowrishankar M C, Pavan Hiremath, Sathyashankara Sharma, Manjunath Shettar, Jayashree P K
In casting alloys Al3XX series, silicon is present in the range of 6–9 wt.%, leading to the formation of intermetallic phases (AlFeSi and alpha-AlFeSi) to its low solubility in aluminum. Iron forms Fe-rich intermetallic phases, which affects the material’s ductility. This effect is even more severe in the presence of Si (Otani et al., 2019). Precipitation hardening can be used as a strengthening mechanism in aluminum alloys containing Cu and Mg elements. Further, better mechanical properties can be obtained by Cu/Mg-rich precipitates at low temperatures while artificial aging (Shi et al., 2021). To reduce the formation of alpha and beta Al intermetallic phases in the microstructure, the following two ways may be used: (i) Increasing the cooling rate during solidification (ii) Increasing the Mn content (Otani et al., 2019). A319 is widely used in various applications because of its castability, good corrosion resistance, and few other properties that make it the first preference for its applications (García-García et al., 2007; Shi et al., 2021). Mechanical properties of A319 alloy depend on SDAS (secondary dendrite arm spacing), Si particles, porosity, inclusions, and some other alloying elements present in it (Kori & Prabhudev, 2011; Mohamed et al., 2012). MMC’s properties and performances depend on the selection of matrix material, reinforcements, processing parameters, and processing techniques (Karbalaei Akbari et al., 2015).
Atomic-scale study of precipitates (NbC and Cu-rich phase) at the twin boundary in the long time ageing austenitic stainless steel
Published in Philosophical Magazine, 2020
Xingyuan San, Dan Zhang, Xinshuang Guo, Xingkun Ning
The precipitated phase is usually small, but it plays an essential role in improving the mechanical properties of alloys and compounds [1,2]. Precipitation hardening, as a classical strengthening mechanism, involves the strengthening of alloys by coherent precipitates. The coherent precipitates are capable of being sheared by dislocations and used to increase the strength of tempered steel and aluminium alloys [3,4]. Besides the precipitation strengthening, the solid solution strengthening and twin boundary strengthening are importance mechanism for mechanics performance [5,6]. Specially, twin boundaries (TBs) are served as effective strategy for strength enhancements without much loss of ductility. For example, ultrahigh density of nanoscale growth twins in fine-grained Cu and stainless steel significantly improved the strength and tensile ductility [7,8]. In addition, element segregation in the grain boundaries especially in TBs also has attracted tremendous interest [9].
Revisit of the shape and orientation of precipitates with tetragonal transformation strains that minimise the elastic energy
Published in Philosophical Magazine, 2020
A. Tordjman, A. Wasserblat, R. Z. Shneck
Precipitation hardening is a very efficient and versatile mechanism of hardening of metals. The shape of the precipitates affects their degree of hardening but also the degree of embrittlement imparted to the alloy. The shape adopted by real precipitates is found to belong to a small group of simple shapes and is believed to be selected so as to minimise the sum of their surface energy and elastic energy. In the present contribution, we determine and explain the selection of shape and orientation relative to a matrix with cubic symmetry of precipitates with tetragonal misfit strains, from elastic energy considerations only. As will be found, the answer to this limited question is already not simple but it is responsible to the main shape-dependent contribution to the energy of precipitates. A tetragonal misfit strain (transformation strain) is defined byand characterised by the tetragonality ratio t = ε3/ε1. The elastic energy in such systems depends on the misfit strain, the shape of the precipitate, its orientation relative to the matrix and the relative elastic constants of the matrix and precipitate. In isotropic materials the relative elastic constants are measured by the ratio between the shear moduli: γ = μm/μp.