Cu-Ni-Si alloys are widely used for electrical applications owing to high strength and high electrical conductivity. In this work, the effects of Cr and Zr additions on microstructure and properties of Cu-Ni-Si alloys were investigated. The addition of Cr and Zr results in formation of Cr 3 Si and Ni 2 SiZr intermetallic compounds, respectively, thus increases the electrical conductivity of Cu-Ni-Si alloy and refines the microstructure. Microstructure analysis confirms the presence of δ-Ni 2 Si precipitates, which strengthens the alloy through Orowan mechanism. Alloying with Zr element deteriorates the mechanical property of Cu-Ni-Si alloy, whereas in the presence of Cr, to the contrary, the ultimate tensile strength is increased, whether Zr is incorporated or not. Moreover, the addition of Zr can decrease the stacking fault energy (SFE) and promote formation of deformation twins. The best integrated performance is obtained through co-addition of Cr and Zr elements. The ultimate strength, elongation and electrical conductivity are 706 MPa, 9.5% and 48.2% IACS, respectively. The precipitation kinetics was discussed in terms of Avrami equation and the activation energy of Ni 2 Si precipitation was obtained. The calculated activation energies of precipitation are 105, 89, 115 and 111 kJ/mol for Cu-Ni-Si, Cu-Ni-Si-Zr, Cu-Ni-Si-Cr and Cu-Ni-Si-Cr-Zr alloy, respectively.

Effects of Cr and Zr additions on microstructure and properties of Cu-Ni-Si alloys

Evaluation of nanoscaled precipitates in a Cu-Ni-Si-Cr alloy during aging

A commercial Cu-Ni-Si-Cr alloy used as a model material was annealed and then peak-aged. The detailed microstructure and property analyses were performed to determine the correlations between the microstructure characteristics and properties. Theoretical calculations, which gave results in good agreement with experimental results, demonstrated that solid-solution scattering and Orowan bypass of precipitate strengthening were the key mechanisms for electrical and mechanical properties, respectively. Furthermore, the effects of composition on the aging behaviors and then electrical and mechanical properties for Cu-Ni-Si series alloys were systematically investigated, showing that both the precipitation extent and mechanical properties improved simultaneously with nominal or effective concentration of the precipitates. Quick estimation on the basis of the present analysis procedure indicates that our work is applicable with high accuracy in real cases.

Correlations between microstructures and properties of Cu-Ni-Si-Cr alloy

Fatigue crack growth behavior of additively manufactured 17-4 PH stainless steel: Effects of build orientation and microstructure

Dual incorporation of SiO2 and ZrO2 nanoparticles into the oxide layer on 6061 Al alloy via plasma electrolytic oxidation: Coating structure and corrosion properties

A high-strength Cu-Ni-Si alloy was developed with the additions of Co and Zr. The aging curve for the alloy was generated using hardness. Electron microscopy studies were conducted to analyze the phases in the alloy. Two types of phases, one of copper matrix and the other of Ni-Si-Co-Zr intermetallic phase, could be identified using scanning electron microscopy. Transmission electron microscopy studies confirmed the presence of two types of precipitates in solution-treated and aged (STA) condition, i.e., Ni2Si and Co2Si. Mechanical properties and electrical conductivity were evaluated in solution-treated (ST) and STA conditions. Aging of the ST samples at 500 °C for 3 h has shown an increase of 72 and 15% in yield strength (YS) and electrical conductivity, respectively. This increase in YS and conductivity on aging is primarily attributed to the formation of fine Ni2Si and Co2Si precipitates.

Microstructure and Properties of a High-Strength Cu-Ni-Si-Co-Zr Alloy

Alumina coating was deposited on AA7020 aluminum alloy by plasma electrolytic oxidation (PEO) method. The corrosion, stress corrosion cracking (SCC) and nano-mechanical behaviors were examined by means of potentiodynamic polarization, slow strain rate test (SSRT) and nano-indentation tests. Potentiodynamic polarization (PP) was used to evaluate the corrosion resistance of the coating and slow strain rate test (SSRT) was used for evaluating the environmental cracking resistance in 3.5% NaCl solution. The mechanical properties (hardness and elastic modulus) were obtained from each indentation as a function of the penetration depth across the coating cross section. The above results were compared with similar PEO coated aluminum and magnesium alloys. Results indicated that PEO coating on AA7020 alloy significantly improved the corrosion resistance. However the environmental cracking resistance was found to be only marginal. The hardness and elastic modulus values were found to be much higher when compared to the base metal and similar PEO coated 7075 aluminum alloys. The fabricated coating also exhibited good adhesive strength with the substrate similar to other PEO coated aluminum alloys reported in the literature

Corrosion and nanomechanical behaviors of plasma electrolytic oxidation coated AA7020-T6 aluminum alloy

Isothermal low cycle fatigue (LCF) properties of Cu-Cr-Zr-Ti alloy were evaluated at different temperatures (300 °C, 450 °C and 600 °C) in high purity argon atmosphere. The cyclic stress response (CSR) was highly dependent on the test temperature. CSR at 300 °C showed primary hardening and secondary hardening at lower strain amplitudes from 0.25% to 0.8% and primary hardening followed by continuous softening at 1.2% strain amplitude. At 450 °C, the alloy exhibited a higher degree of primary hardening followed by saturation of stress. Transmission electron microscopic observations made on the samples tested upto different number of cycles indicate that precipitation of fine Cr precipitates was the main reason for the secondary hardening at 300 °C and extensive primary hardening at 450 °C. Even though precipitation was assisted by mechanical working during cycling, it is observed that the secondary hardening occurred almost at the same time irrespective of the strain amplitude used in the tests. At 450 °C and higher strain amplitudes, precipitates nucleated at the dislocations within a few initial cycles causing pinning of the dislocations thereby increasing the stress response. CSR at 600 °C showed continuous softening without any hardening. It is found that the precipitates nucleated during heating and soaking at the test temperature itself before the start of the strain cycling and coarsening of precipitates as well as loss of coherency with the matrix caused continuous softening at 600 °C. With an increase in test temperature, a reduction in fatigue life is observed and the life reduction is significant at higher strain amplitudes. Microstructural observations and fractographic studies indicated that cracks initiated predominantly at surface and propagated inward. Intergranular cracking was observed at higher strain amplitudes at all temperatures.

Effect of temperature on low cycle fatigue behavior of annealed Cu-Cr-Zr-Ti alloy in argon atmosphere

Precipitation hardenable stainless steels are widely used in aerospace applications because of their excellent combination of strength and corrosion resistance. In view of this advantage, Fe-17Cr-4Ni (17-4 PH) steel is used in pyro bolts in space ordnance systems for stage separation in a satellite launch vehicle. These systems typically consist of a pyro charge to sever a given material resulting in stage separation, and these materials are exposed to high strain rates. In one such application, although perfect severance took place, secondary cracks were noticed longitudinally, which are not desirable. This steel, in view of its composition, has delta ferrite in a martensitic matrix in the hardened and tempered condition. In wrought products worked unidirectionally, delta ferrite gets oriented along the direction of thermomechanical processing. The effect of delta ferrite orientation on the impact properties of 17-4 PH stainless steel was studied in various heat-treatment conditions with a view to understand the effect of microstructure on impact properties. It was found that the transverse impact properties are severely affected by the presence of highly oriented delta ferrite stringers for any given heat-treatment condition. This has been attributed to the weak delta ferrite–martensite interface, which facilitates easy crack propagation. Finally, it was suggested that the anisotropy in impact properties need to be carefully considered in the design of components for applications that involve high strain rates.

Metallurgical Analysis of a Failed 17-4 PH Stainless Steel Pyro Bolt Used in Launch Vehicle Separation Systems

In this investigation, a precipitation hardenable martensitic stainless steel (12Cr–10Ni–0.25Ti–0.7Mo) was subjected to different heat treatment cycles to study their influence on the microstructure and mechanical properties. The heat treatment cycles include solution treatment (S), cryogenic treatment (C), and aging (A). Two solution treatment temperatures, 750 and 1000 °C, and two aging temperatures, 250 and 500 °C, were selected. Solution treatment was followed by a cryogenic treatment at −70 °C for 2 h and an aging treatment at the aforementioned temperatures. Transmission electron microscopy of the solution-treated samples showed four phases: martensite matrix, M23C6 carbide, Ti(C, N), and retained austenite. On aging at 500 °C, an additional phase (Ni3Ti precipitates) was observed in the martensite matrix. Mechanical properties were evaluated at room temperature for all the heat-treated samples. A reasonable increase in yield strength (YS) was observed after cryogenic treatment possibly due to transformation of retained austenite to martensite. After aging at 500 °C, a significant increase in the YS was observed over solution-treated condition. This increase in YS after aging is attributed to precipitation of fine Ni3Ti precipitates. Solution treatment temperature had an insignificant effect on the mechanical properties of the stainless steel.

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J. Srinath

Papers

Microstructure and Properties of a High-Strength Cu-Ni-Si-Co-Zr Alloy

Corrosion and nanomechanical behaviors of plasma electrolytic oxidation coated AA7020-T6 aluminum alloy

Effect of temperature on low cycle fatigue behavior of annealed Cu-Cr-Zr-Ti alloy in argon atmosphere

Metallurgical Analysis of a Failed 17-4 PH Stainless Steel Pyro Bolt Used in Launch Vehicle Separation Systems

Effect of Heat Treatment on Microstructure and Mechanical Properties of 12Cr–10Ni–0.25Ti–0.7Mo Stainless Steel