Ningbo Branch of China Ordnance Academy

Ningbo, China

Ningbo Branch of China Ordnance Academy

Ningbo, China
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Niu H.Z.,Northwest Institute for Nonferrous Metal Research | Chen Y.F.,Ningbo Branch of China Ordnance Academy | Zhang D.L.,Shanghai JiaoTong University | Zhang Y.S.,Northwest Institute for Nonferrous Metal Research | And 3 more authors.
Materials and Design | Year: 2016

This study deals with preparing powder metallurgy Ti2AlNb-based alloy via spark plasma sintering (SPS) technique. A pre-alloyed Ti2AlNb-based alloy powder was produced by a plasma rotating electrode process (PREP), and then consolidated using SPS at temperatures between 900°C and 1050°C with a pressure of 50MPa. Most of the pre-alloyed powder particles are characterized by single B2-phase dendrites. When the SPS temperature was 1000°C or higher, the dendritic features and original boundaries of powder particles were removed, resulting in fully dense compacts. The as-sintered microstructure was modified by heat treatment to form fine acicular O-precipitates, leading to a superior yield strength of up to 1220MPa at room temperature (RT). On the other hand, the heat treated microstructure with coarsened O-precipitates, produced via controlled slow cooling within the B2+O phase field, exhibits a good RT elongation to fracture of 9.5%, but a relatively low yield strength of 840MPa. © 2015 .


Chen Y.F.,Zhejiang University | Chen Y.F.,Ningbo Branch of China Ordnance Academy | Chen Y.,Harbin Institute of Technology | Tu J.P.,Zhejiang University | Zheng S.Q.,Ningbo Branch of China Ordnance Academy
Advanced Materials Research | Year: 2014

γ-TiAl alloys are emerging as potential light-weight, high-temperature structural materials and possess wide capacities of engineering applications in aeronautics, space and automobile industries because of their low density, high specific strength and specific modulus, good oxidation-resistance and creep-resistance. Investment casting is introduced to complex TiAl net-shape or near net-shape components. In this research, ZrO2 (CaO stabilized) was chosen as the face coat materials for the investment casting of TiAl alloys. The present study mainly focuses on the fabrication of ceramic shell mould for TiAl investment casting. Optimisation of reducing the stress in cast-mould system was carried out. The processing technology of the invented ceramic shell moulds was successfully verified in the investment casting of prototype TiAl parts. The interfacial reaction between TiAl alloys and ZrO2 ceramic mould was analyzed using OM, SEM, EDS and XRD. The experimental results showed that, when the rotation speed is 200 rpm and 400 rpm, the thickness of reaction layer is about 5μm and 20μm, respectively. © (2014) Trans Tech Publications, Switzerland.


Zhou L.Z.,Ningbo University | Zhou L.Z.,Ningbo Branch of China Ordnance Academy | Yang L.M.,Ningbo University | Peng Y.J.,Ningbo Branch of China Ordnance Academy | Zhu X.R.,Ningbo Branch of China Ordnance Academy
Applied Mechanics and Materials | Year: 2014

Fe-Cr-Ni preform reinforcing aluminum composite was produced by squeeze casting. And then, T6 heat treatment was conducted to enhance the composite’s performance. After which, isothermal compression tests in temperature range of 298 - 473 K at an strain rate range from 0.001 to 10 s-1 were carried out on Gleeble 3500 thermo-mechanical simulation machine. It is found that, for a specific strain rate, the flow stress decreases markedly with temperature increases. And for a fixed temperature, the flow stress generally increases as the strain rate increases. Based on the experimental true stress-true strain data, the Arrhenius type model was established. © (2014) Trans Tech Publications, Switzerland.


Zhou L.Z.,Ningbo University | Yang L.M.,Ningbo University | Zhou L.Z.,Ningbo Branch of China Ordnance Academy | Peng Y.J.,Ningbo Branch of China Ordnance Academy | Zhu X.R.,Ningbo Branch of China Ordnance Academy
Applied Mechanics and Materials | Year: 2014

In this paper, squeeze casting process was adopted to produce the Fe-Cr-Ni preform reinforced Al-Si-Cu-Ni-Mg aluminum composite. And then, T6 heat treatment was conducted to enhance the composite’s performance. After which, isothermal compression tests in temperature range of 473 -773 K at an interval of 150 K and strain rate range from 0.001 to 10 s-1 were carried out on Gleeble 3500 thermo-mechanical simulation machine. It is found that, for a specific strain rate, the flow stress decreases markedly with temperature increases. And for a fixed temperature, the flow stress generally increases as the strain rate increases. Based on the experimental true stress-true strain data, the Arrhenius type model was established. © (2014) Trans Tech Publications, Switzerland. All Rightsa Reserved.


Wang J.,Ningbo Branch of China Ordnance Academy | Wang J.,Zhejiang University | Nie J.-J.,Ningbo Branch of China Ordnance Academy | Wang R.,Ningbo Branch of China Ordnance Academy | And 3 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2012

Ageing hardening, microstructure and mechanical properties of Mg-xY-1.5LPC-0.4Zr (x=0, 2, 4, 6) alloys (LPC represents La-based rare earth metal) were investigated. It was found that the age hardening was enhanced, the grains became finer and the tensile strength was improved with the increase of Y content in Mg-Y-1.5LPC-0.4Zr alloy. The results show that the formed precipitates responsible for age hardening change from fine hexagonal-shaped equilibrium Mg 12RE phase to metastable β′ phase with orthorhombic-bc crystal structure when Y is added into Mg-1.5LPC-0.4Zr alloy, and the volume fraction of precipitate phases also increases. The cubic-shaped β-Mg 24Y 5 precipitate phases were also observed at grain boundaries in Mg-6Y-1.5LPC-0.4Zr alloy. The distribution of prismatic shaped β′ phases and cubic shaped β-Mg 24Y 5 precipitate phases in Mg matrix may account for the remarkable enhancement of tensile strength of Mg-Y-LPC-Zr alloy. The Mg-6Y-1.5LPC-0.4Zr alloy exhibits maximum tensile strength at peak-aged hardness, and the values are 250 MPa at room temperature and 210 MPa at 250°C. © 2012 The Nonferrous Metals Society of China.


Shao Z.,Zhejiang University | Shao Z.,Ningbo Branch of China Ordnance Academy | Zhu X.,Ningbo Branch of China Ordnance Academy | Wang R.,Ningbo Branch of China Ordnance Academy | And 4 more authors.
Materials and Design | Year: 2013

The hot deformation behavior of a newly developed as-homogenized Mg-9d-3Y-2Zn-0.5Zr (GWZ932) magnesium alloy has been investigated with Gleeble-3500 thermal simulator. Compression tests were performed in the temperature range of 410-470°C and in the strain rate ranging from 0.01s-1 to 10s-1. The stress-strain behavior has been studied and it was found that the form of the flow stress curves was sensitive to temperature and strain rate. The processing map at the strain of 0.5 which represented steady-state flow was developed by plotting the variation of the efficiency of the power dissipation as a function of temperature and strain rate. Both safety deformation domain and instability regions were identified in the processing map. The microstructures evolution and dynamic recrystallized (DRX) were also analyzed and discussed. The results showed that the optimum hot working condition for the alloy, which has been determined based on the processing map and microstructures evolution, was deformation at the temperature of 450°C with the strain rate of 0.01s-1. © 2013 Elsevier Ltd.


Zhu X.,Ningbo Branch of China Ordnance Academy | Wang J.,Ningbo Branch of China Ordnance Academy | Xu Y.,Ningbo Branch of China Ordnance Academy | Wang R.,Ningbo Branch of China Ordnance Academy | And 2 more authors.
Journal of Rare Earths | Year: 2013

Microstructure and creep behaviour of Mg-12Gd-3Y-1Zn-0.4Zr alloy prepared by squeeze casting were investigated. Transmission electron microscope (TEM) observation revealed that a kind of lamellar-shaped morphologies 14 h long-period stacking order structure (LPSO) and dense βk'-phase precipitates were formed by heat treatment. The alloy exhibited good creep resistance. It was shown that the creep-resistant performance kept stable because of the restriction of dense β'-phase precipitates and LPSO phases to the movement of dislocations, and the formation of β-phase plates took responsibility for the softening of material during creep. Stress and temperature dependence of the steady-state creep rate were studied over stress range of 50-100 MPa and a temperature range of 250-300°C, and a dislocation creep mechanism was proposed for the alloy. © 2013 The Chinese Society of Rare Earths.


Wang R.,Ningbo Branch of China Ordnance Academy | Zhu X.R.,Ningbo Branch of China Ordnance Academy | Shao Z.W.,Ningbo Branch of China Ordnance Academy | Xu Y.D.,Ningbo Branch of China Ordnance Academy | And 3 more authors.
Materials Science Forum | Year: 2014

Magnesium wrought alloys are of special interest for structural components owing to their improved microstructures and mechanical properties by comparison with Mg cast parts. However, the market of Mg wrought alloys is still relatively small and one of the most important limitations for their application in areas such as aviation and spaceflight is that their strength is still not high enough to be widely used. Currently, more and more attention are paid to hydrostatic extrusion of Mg alloys because the extruded Mg alloys which exhibit extremely fine grains and high strength can be easily obtained by hydrostatic extrusion process. This review detailed the microstructures and mechanical properties of various wrought Mg alloys subjected to hydrostatic extrusion. Furthermore, numerical simulations and processing parameters optimization of the hydrostatic extrusion were also discussed. Finally, the current problems and development trends of hydrostatic extrusion of high-strength Mg alloys were also put forward. © (2014) Trans Tech Publications, Switzerland.


Xu Y.D.,Ningbo Branch of China Ordnance Academy | Wang J.,Ningbo Branch of China Ordnance Academy | Shao Z.W.,Ningbo Branch of China Ordnance Academy | Wang R.,Ningbo Branch of China Ordnance Academy | Zhu X.R.,Ningbo Branch of China Ordnance Academy
Materials Science Forum | Year: 2014

Microstructures and mechanical properties of Mg-10Gd-3Y-2Zn-0.5Zr alloy were investigated. Three kinds of phases including Mg, Mg3(GdYZn) and Mg12(GdY)Zn were found in the as-cast alloy. Two different patterns of the long-period stacking order (LPSO) phases including lamellar structure and block-like structure were observed in the homogenized alloy and both of them were identified as the phase of Mg12(GdY)Zn. After extrusion with ratio of 10:1 under 420°C, fine dynamic recrystallized grains were obtained and its average size was only about 4μm. The alloy exhibited excellent mechanical properties by hot extrusion and heat treatment. The ultimate tensile strengths of the as-extruded and peak-aged alloys were 415MPa and 480MPa, the tensile yield strength were 335MPa and 410MPa, the elongations were 16% and 13.5%, respectively. The high mechanical properties were mainly attributed to the combined effects of fine grains, LPSO phases and the dispersed precipitates. © (2014) Trans Tech Publications, Switzerland.


Niu H.Z.,Northwest Institute for Nonferrous Metal Research | Chen Y.F.,Ningbo Branch of China Ordnance Academy | Zhang Y.S.,Northwest Institute for Nonferrous Metal Research | Lu J.W.,Northwest Institute for Nonferrous Metal Research | And 2 more authors.
Materials and Design | Year: 2016

This study deals with phase transformation and dynamic recrystallization (DRX) behavior of a β-solidifying alloy Ti-45Al-4Nb-2Mo-B (at.%). Its phase transformation and DRX modes strongly depended on temperature/specific phase field. At low forging temperature within α/α2+γ+B2/β phase field, decomposition of lamellar structures via L(α/γ)→γ+β along with DRX of γ and B2/β grains prevailed around prior α/γ colony boundaries. Conversely, when forging close to α-transus (Tα), closely following quick transition of γ+B2/β→α, DRX was totally localized within α grains. All these processes could be promoted greatly by lowering strain rate. Based on this study, large-scale forging and its microstructural design were realized successfully. Besides anisotropic flow behavior of prior lamellar structures, insufficient decomposition time was also considered as the reason of remnant lamellar structures. Finally, post-forging annealing and an alternative superplastic straining within α2+B2/β+γ phase field were proposed to entirely eliminate the remnant lamellar structures, in order to produce full fine-grained B2/β+γ microstructure. © 2015.

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