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Aluminum-Copper alloys are widely utilized in military, aerospace and aircraft industries for its light weight, excellent castability, superior corrosion resistance, as well as high specific strength after solution, quenching and age hardening treatments. However, the distortion occurring in the quenching process limits its application, especially for the large scale complicated workpieces. In this study, a novel duplex treatment combining the coating and nitriding is applied to the sections of the thin-wall barrel that easy to deform during quenching. The results show that a gradient multiphase layer, consisting of two different regions, is shaped on the thin-wall sections easy to deform. The phase compositions of the surface and subsurface layer are dominated by TiN 0.3 and Al 3 Ti, respectively. The Young's modulus of the TiN 0.3 and Al 3 Ti are 199 GPa and 196 GPa respectively. While, the microhardness for both the two phases are 6.19 GPa and 4.24 GPa respectively, which are much higher than that for the aged ZL205A alloy substrate. The finite element method (FEM) simulation results show that the maximum temperature difference, thermal stress, residual stress as well as deformation of the thin-wall barrel workpiece are reduced due to the multiphase layer. Consequently, the maximum radial deformation of the workpiece can be reduced 96% due to the superior strength and hardness as well as heat conduction of the gradient multiphase layer. • Quenching deformation occurs on the thin-wall sections of the barrel according to the FEM simulation. • The gradient multiphase layer is prepared on the thin-wall sections by deposition titanium film and nitriding. • The phase composition of the multiphase layer is dominated by TiN 0.3 and Al 3 Ti. • The much higher heat conductivity and superior strength and hardness of the multiphase layer results in 96% reduction of the workpiece. [ABSTRACT FROM AUTHOR]

Microstructure and mechanical properties of a quenched M50 steel plasma nitrided for 8 h at temperatures ranging from 480 to 540 °C in a gas mixture of 25% N 2  + 75% H 2 were investigated in this paper. Results show that, compared with the original specimen, microhardness and wear resistance of M50 steel after nitriding treatment are remarkably improved at various temperatures, wherein the N500 specimen achieved the optimum combination of surface hardness (1186 HV), substrate hardness (643HV) and wear resistance (wear rate reduced by 90% more than original specimen). Such significantly improvement could mainly be attributed to the formation of nanophase FeN 0.076 , occurrence of further secondary hardening of substrate and generation of a nitrided surface layer of M50 steel during nitriding process. Two types of carbides, identified as MC and M 6 C, were found to be the stable precipitates present in substrate of N500 specimen. These results provide us with an attractive method of combining nitriding with secondary hardening to achieve a comprehensive performance from surface to substrate of M50 steel. [ABSTRACT FROM AUTHOR]

Dual magnetron sputtering and thermo plasma nitriding were performed to fabricate Cu-Ti-N coating on the surface of Cu substrate, and the microstructure formation and evolution mechanism were investigated. The results showed that the composition of the Cu-Ti coating could be tuned to be around Cu:Ti = 1:1.2 by the appropriate choice of sputtering power for the dual targets, and only amorphous Cu-Ti phases formed. During the thermo plasma nitriding process, crystalline CuTi and Cu 3 Ti occurred. Moreover, a nitride layer of about 0.3 μm containing nanocrystalline TiN formed on the surface, and the multi-phase coating developed to be about 4 μm, which could provide better support for the nitrided layer. [ABSTRACT FROM AUTHOR]

To improve the mechanical properties of C61900 copper–aluminum alloy, a multi-phases coating was fabricated by the combination of thermo-diffusing Ti film and plasma nitriding. The results showed that a smooth coating with fine and uniform grains could be achieved, and the 9 μm thick multi-phases coating, containing Ti–Cu–Al intermetallics (CuTi 2 , CuTi, AlCu 2 Ti) and titanium nitride (Ti 2 N) formed on the nitrided surfaces. The surface hardness of the coating was obviously improved to be 630 HV 0.01 , and the cross-sectional hardness decreased gradually to that of C61900 Cu–Al alloy. Moreover, the wear rate of the coated specimen decreased significantly, dropping 95.5% compared with the untreated Cu–Al alloy. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, martensite transformation induced by plasma nitrocarburizing in AISI304 austenitic stainless steel is investigated. The optical micrographs and XRD results indicate the dual-layer structure of the nitrocarburized layer: the outer martensite transformation layer and the inner C supersaturated austenite layer. The initial transformation microstructure presents as nanoscale qusai-pealite which is composed of α′-martensite and NaCl-type MX (M = Cr, Mn, Fe, Ni; X = C, N) phase. The martensite transformation layer possesses high hardness and good ductility. [Copyright &y& Elsevier]

Highlights: [•] A novel duplex surface treatment on 2024 Al alloy was proposed. [•] A multiphase layer composed of TiN0.3, Al3Ti and Al18Ti2Mg3 was prepared on the surface of 2024 Al alloy. [•] The microstructures of TiN0.3, Al3Ti and Al18Ti2Mg3 were characterized by SEM and TEM. [•] The surface hardness of the multiphase layer reached to 590 HV0.01, five times harder than 2024 Al alloy. [•] The wear resistance of 2024 Al alloy was improved significantly. [ABSTRACT FROM AUTHOR]

Abstract: By means of magnetron sputtering method, pure Ti film with thickness of 1.25 μm was deposited on the surface of 5083 Al alloy specimens. The specimens were heated by ion bombardment in a plasma nitriding unit employing a mixed gas of N2 and H2 at 460 °C for 16 h. The treated surface layers of specimens were characterized by using SEM equipped with EDS, TEM, XRD analysis and nanoindentation as well as potentiodynamic polarization tests. The results show that the Al18Ti2Mg3 layer with a thickness of 6.3 μm can be formed on the surface of the specimens during interdiffusing of Ti, Mg and Al across the interface between Ti film and the substrate alloy. The interdiffusion layer possesses much higher Young's modulus (131 GPa), the nanohardness (8.97 GPa) and corrosion potential (−0.75VSCE) than those of 5083 Al–Mg alloy. Additionally, the Al18Ti2Mg3 phase layer has an excellent plastic deformation ability resulting mainly from its plasticity deformation power dissipation ratio (η p) up to 87%. [Copyright &y& Elsevier]

Highlights: [•] We study the interaction between lanthanum and nitrogen during plasma nitriding. [•] The addition of pure lanthanum could reduce the nitrogen content in the surface layer. [•] There is an attractive function between lanthanum and nitrogen. [Copyright &y& Elsevier]

Abstract: In the present study, low temperature plasma nitriding of nanocrystallized 18Ni maraging steel has been carried out at 360°C from 1 to 24h in a mixed gas of 25%N2 +75%H2. The surface phase constitutions and microstructures of the nitrided layer have been investigated by X-ray diffraction analysis, transmission electron microscopy and optical microscopy. Nanoindentation and microhardness tests have been performed to determine the surface hardness and the hardness profile in the nitrided layer. The plasticity of the nitrided surface has been analyzed based on the nanoindentation results. The results show that at the initial stage of nitriding, the surface phase consists of a solid solution of nitrogen in α-Fe, and nanoscale nitrides and aging phase are formed with increasing of treatment time. The surfaces nitrided for 8 and 16h possess the highest hardness. The plasticity factor calculations suggest that the nitrided surfaces have a good wear resistance and possess excellent plasticity. [Copyright &y& Elsevier]

Abstract: 17-4PH stainless steel was plasma nitrocarburized at 460°C for improving its mechanical properties without compromising its desirable corrosion resistance. The plasma nitrocarburized layers were studied by optical microscope, X-ray diffractometer, microhardness tester, pin-on-disc tribometer and the anodic polarization method in a 3.5% NaCl solution. The experimental results show that the nitrocarburized layer depths increase with increasing duration time and the layers growth conform approximately to the parabolic law. The phases in the nitrocarburized layer are mainly of γ′-Fe4N and α′-Fe with traces of CrN phase. The surface hardness of the modified specimen is more than 1200HV, which is three times higher than that of untreated one. The friction coefficient and corrosion resistance of the specimen can be apparently improved by plasma nitrocarburizing. With the increase of duration time, the surface hardness slightly decreases whereas the friction coefficient and corrosion resistance of the modified specimen are first increase and then decrease. The 8h treated specimen has the lowest friction coefficient and the best corrosion resistance in the present test conditions. [Copyright &y& Elsevier]

Abstract: 18Ni-maraging steel has been entirely nanocrystallized by a series of processes including solution treatment, hot-rolling deformation, cold-drawn deformation and direct electric heating. The plasma nitriding of nanocrystallized 18Ni-maraging steel was carried out at 410°C for 3h and 6h in a mixture gas of 20% N2 +80% H2 with a pressure of 400Pa. The surface phase constructions and nitrogen concentration profile in surface layer were analyzed using an X-ray diffractometer (XRD) and the glow discharge spectrometry (GDS), respectively. The results show that an about 2μm thick compound layer (mono-phase γ′-Fe4N) can be produced on the top of the surface layer of nanocrystallized 18Ni-maraging steel plasma nitrided at 410°C for 6h. The measured hardness value of the nitrided surface is 11.6GPa. More importantly, the γ′-Fe4N phase has better plasticity, i.e., its plastic deformation energy calculated from the load-displacement curve obtained by nano-indentation tester is close to that of nanocrystallized 18Ni-maraging steel. Additionally, the mechanical properties of γ′-Fe4N phase were also characterized by first-principles calculations. The calculated results indicate that the hardness value and the ratio of bulk to shear modulus (B/G) of the γ′-Fe4N phase are 10.15GPa and 3.12 (>1.75), respectively. This demonstrates that the γ′-Fe4N phase has higher hardness and better ductility. [Copyright &y& Elsevier]

In this work, we studied the microstructure formation and mechanical properties of the Ti alloyed C17200 Cu surface produced by plasma nitriding at 750 °C. The results firstly show that the multiphase coating consists of amorphous and nano-crystalline phases, and various types of Cu-Ti intermetallics, including CuTi 2 , CuTi, Cu 3 Ti 2 , Be 3 Ti 2 Cu, Cu 2 Ti, Cu 3 Ti, formed after the plasma nitriding at 750 °C. The formation of the specific type of Cu-Ti intermetallic depends on the processing duration, where a longer duration contributes to the formation of intermetallics with a higher Cu/Ti ratio. The evolution of the phase compositions is responsible for the change in the mechanical properties. The surface hardness of the modified C17200 Cu alloy improves to be 400 HV 0.01 to a depth of 15 μm after plasma nitriding for 6 h, which contributes to a higher surface tribological resistance with a friction coefficient of 0.3 and a wear rate of 4.15 × 10 −9 g/(r·N) for the modified suface. [ABSTRACT FROM AUTHOR]

Theoretical and experimental methods are utilized to design and prepare the expanded martensite (α′ N ) on the steel 38CrMoAl by plasma nitriding. Lehrer diagram is firstly calculated by thermodynamic method, based on which the plasma nitriding experiments are conducted to prepare single-phase α′ N layer. Microstructure and mechanical properties for α′ N layer are further characterized by XRD, TEM and nanoindentation methods. Results show that an expected single-phase α′ N layer is obtained by nitriding at 590 °C in atmosphere with the nitrogen-hydrogen flow ratio of 0.05:0.4. Moreover, single-phase α′ N layer is also detected beneath the outermost compound layer about 20 μm thick in 460 °C nitrided layer. The maximal peak offset of 0.5° and broadening for α′ N (110) indicate that the supersaturated N dissolved in refined grains. Ultra-refined grains about ~ 10 nm of α′ N observed by TEM, elucidate the nano-crystalline layer can be obtained by one-step low-temperature plasma nitriding at 460 °C. However, no evident refinement for α′ N is observed in the 590 °C nitrided layer. More importantly, compare with the γ′-Fe 4 N and ε-Fe 2 − 3 N, significantly improved H and the ratios of H/E and H 3 /E 2 of α′ N layer demonstrate its superior hardness, strength and toughness. [ABSTRACT FROM AUTHOR]

In this work, quenched AerMet100 steel is plasma nitrided at 460 °C for 8 h in a gas mixture of 50% N 2 + 50% H 2. The microstructures and mechanical properties are investigated. Results show that the current nitriding conditions can effectively inhibit the formation of brittle white compound layer in the surface of AerMet100 steel. Further investigations on orientations of martensite laths and prior austenite confirm that all 24 variants of martensite laths produced by one prior austenite grain follow the K S orientation relationship and this relationship holds during nitriding. Besides, a memory phenomenon that the orientation of precipitated γ′-Fe 4 N is exactly the same as that of prior austenite is observed, due to the strong variant selection. Compared with the un-nitrided specimen, the microhardness of AerMet100 steel after nitriding treatment is remarkably improved, and volume wear rate is reduced by an order of magnitude. Such a large improvement is primarily attributed to a desirable combination of high surface hardness, considerable nano-grains and secondary hardening of the substrate. Unlabelled Image • Brittle layer is avoided, with hardened substrate and improved wear resistance achieved. • K S OR between lath martensite and prior austenite holds during nitriding. • There is an orientation memory phenomenon between γ′-Fe 4 N and prior austenite. [ABSTRACT FROM AUTHOR]