EFFECT OF VACUUM HEAT TREATMENT ON OXIDATION BEHAVIOR OF SPUTTERED NiCrAlY COATING

A bond coat for thermal barrier coating (TBC), NiCrAlY coating, is subjected to vac-uum heat treatment in order to remove internal stress before ceramic top coat is de-posited. The effect of vacuum heat treatment on the oxidation behavior of the sputtered NiCrAlY coating has been investigated. The as-sputtered NiCrAlY coating consists of γ-Ni and b-NiAl phases. After vacuum heat treatment, the sputtered NiCrAlY coating mainly consists of γ'-Ni3Al, β-NiAl, γ-Ni, and trace of α-Al2O3 phases. The isothermal oxidation of sputtered NiCrAlY coating with and without vacuum heat treatment has been performed at 1000℃. It is shown that a-Al2O3 formed during vacuum heat treatment acts as nuclei for the formation of a-Al2O3, and the protective a-Al2O3 scale is formed more rapidly on the vacuum heat treated NiCrAlY coating than that formed on the untreated coating. Also the a-Al2O3 scale has a better adherence to the vacuum heat treated NiCrAlY coating. Therefore the vacuum heat treatment improves the oxidation resistance of sputtered NiCrAlY coating.

Synergistic effects of composition and heat treatment on microstructure and properties of vacuum die cast Al-Si-Mg-Mn alloys

The purpose of this study was to prepare high-quality Al-Si-Mg-Mn alloy with a good combination of strength and ductility employing the vacuum-assisted high-pressure die cast process. An orthogonal study of heat treatments was conducted to design an optimized T6 heat treatment process for both Al-10%Si-0.3%Mg-Mn and Al-11%Si-0.6%Mg-Mn alloys. The results demonstrate that no obvious blisters and warpage were observed in these two alloys with solid solution treatment. After the optimal T6 heat treatment of 530°C×3 h + 165°C×6 h, Al-11%Si-0.6%Mg-Mn alloy has better mechanical properties, of which tensile strength, yield strength and elongation reached 377.3 MPa, 307.8 MPa and 9%, respectively. The improvement of mechanical properties can be attributed to the high density of needle-like β″(Mg_5Si_6) precipitation after aging treatment and the fine and spherical eutectic Si particles uniformly distributed in the α-Al matrix.

A CMOS Compatible MEMS Pirani Vacuum Gauge with Monocrystal Silicon Heaters and Heat Sinks

We present a micro-Pirani vacuum gauge using the low-resistivity monocrystal silicon as the heaters and heat sinks fabricated by the post complementary metal oxide semiconductor （CMOS） microelectromechanical system （MEMS） process. The metal interconnection of the device is fabricated by a 0.5 μm standard CMOS process on 8-inch silicon wafer. Then, a SiO2-Si low-temperature fusion bonding is developed to bond the CMOS wafer and the MEMS wafer, with the electrical connection realized by the tungsten through silicon via process. Wafer- level A1Ge euteetic bonding is adopted to package the Pirani gauge in a non-hermetic cavity to protect the gauge from being damaged or contaminated in the dicing and assembling process, and to make it suitable for actual applications. To increase the accuracy of the test and restrain negative influence of temperature drift, the Wheatstone bridge structure is introduced. The test results show that before capping, the gauge has an average sensitivity of 1.04 × 104 K.W-1Torr-1 in dynamic range of 0.01 20 Torr. After capping, the sensitivity of the gauge does not decrease but increases to 1.12 × 104 K.W-1 Torr-1.

An ingenious approach of determining hydrogen isotope solubilities, diffusivities and permeabilities in GWHER-1 stainless steel

In this paper, by using an ingenious method, the hydrogen isotope solubilities and diffusivities in GWHER-1 stainless steel have been determined by a vacuum heating degassing approach at the temperature range of 597-1022 K on a set of specimens with different sizes previously charged for 24 h under a hydrogen isotope pressure of 105 Pa in the temperature range of 800-1000 K. The permeabilities are then derived from the relation Φ = DKs. It is found D = 1.52 ×10^-6exp（-54100/RT）, Ks = 2.2×10^-exp（-5400/RT） and Φ = 3.3 ×10^-12exp（-59500/RT） for hydrogen, where Ks （Sieverts＇ constant） is given in Pa^-1/2, D in m2.s^-1.Pa^-1/2, T in K and R=8.31 J.mol^-1.K^-1. By taking isotope effects into account, the corresponding Arrhenius relations for deuterium and tritium are also deduced.

Behavior of NiCrAlY coating on the TC6 titanium alloy

A NiCrAlY coating was deposited on the TC6 titanium substrate by arc ion plating （ALP）. The structure and morphologies of the NiCrAlY coating were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）, and the influence of vacuum heat treatment on the element diffusion behavior was studied. The results showed that the y＇-Ni3Al phase was precipitated on the NiCrAlY coating after heat treatment. The Ni3（AI,Ti）, TiNi, and Ti2Ni intermetallic layers appeared at the interface from the outside to the inside at 700℃, and the thickness of the intermetallic layers increased with the increase in temperature. At 700℃ Ti and Ni were the major diffusion elements, and the diffusion of Cr was observed when the heat treatment temperature increased up to 870℃. The violent inward diffusion of Ni at 950℃ resulted in the degradation of the NiCrAlY coating.

Manufacturing and High Heat Flux Testing of Brazed Flat-Type W/CuCrZr Plasma Facing Components

Water-cooled flat-type W/Cu Cr Zr plasma facing components with an interlayer of oxygen-free copper（OFC） have been developed by using vacuum brazing route.The OFC layer for the accommodation of thermal stresses was cast onto the surface of W at a temperature range of 1150oC-1200 oC in a vacuum furnace.The W/OFC cast tiles were vacuum brazed to a Cu Cr Zr heat sink at 940 oC using the silver-free filler material Cu Mn Si Cr.The microstructure,bonding strength,and high heat flux properties of the brazed W/Cu Cr Zr joint samples were investigated.The W/Cu joint exhibits an average tensile strength of 134 MPa,which is about the same strength as pure annealed copper.High heat flux tests were performed in the electron beam facility EMS-60.Experimental results indicated that the brazed W/Cu Cr Zr mock-up experienced screening tests of up to 15 MW/m^2 and cyclic tests of 9 MW/m^2 for 1000 cycles without visible damage.

Effect of vacuum heat treatment on microstructure and corrosion behavior of HVOF sprayed AICoCrFeNiCu high entropy alloy

To improve the corrosion resistance of coalbed methane drilling equipment,an AICoCrFeNiCu high entropy alloy coating was prepared on the AISI 4135(35CrMo)steel substrate by high velocity oxygen fuel(HVOF)technology,and the coating was subjected to vacuum heat treatment(VHT)at different temperatures(500,700,900 and 1100℃).The corrosion test of the substrate and the coatings after VHT in coalbed methane drilling fluid was carried out.The results show that the HVOF sprayed AICoCrFeNiCu high entropy alloy(HEA)coating has a good bonding with the substrate,and the porosity of the coating is about 2.4%.There is partial segregation in the coating,and the coating mainly consists of body-centered cubic phase.The coating has good thermal stability,and the phase structure and microstructure of the coatings have changed after VHT at different temperatures.Compared with the substrate,the as-sprayed coating has better uniform corrosion resistance,and the corrosion resistance of the coating after VHT is further improved.After VHT at 500℃,the HVOF-sprayed AICoCrFeNiCu HEA coating has the best corrosion resistance.

Influence of laser re-melting and vacuum heat treatment on plasma-sprayed FeCoCrNiAl alloy coatings

FeCoCrNiAl high entropy alloy coatings were prepared by supersonic air-plasma spraying.The coatings were post-treated by vacuum heat treatment at 600 and 900°C,and laser re-melting with 300 W,respectively,to study the influence of different treatments on the structure and properties of the coatings.The phase constitution,microstructure and microhardness of the coatings after treatments were investigated using X-ray diffraction,scanning electron microscopy and energy dispersive spectrometry.Results showed that the as-sprayed coatings consisted of pure metal and Fe-Cr.The AlNi;phase was obtained after the vacuum heat treatment process.A body-centered cubic structure with less AlNi;could be found in the coating after the laser re-melting process.The average hardness values of the as-sprayed coating and the coatings with two different temperature vacuum heat treatments and with laser re-melting were 177,227,266 and 682 HV,respectively.This suggests that the vacuum heat treatment promoted the alloying process of the coatings,and contributed to the enhancement of the coating wear resistance.The laser re-melted coating showed the best wear resistance.

Microstructure,mechanical properties and first-principle analysis of vacuum die-cast Mg-7Al alloy with Sn addition

The influences of Sn element and heat treat-ment on the microstructure and mechanical properties of Mg-7Al alloy prepared by vacuum die cast(VDC)were studied.The results indicate thatα-Mg dendrite and Mg_(17)Al_(12) are refined and new Mg_(2)Sn phase is formed in Mg-7Al alloy with 2 wt%Sn addition.The ultimate tensile strength(σ_(b))of Mg-7Al alloy increases from 205 to 258 MPa(i.e.,a 25%increase).The mechanical properties of Mg-7Al-2Sn(AT72)alloy are further improved through heat treatment because of the dense microstructures processed by VDC.In particular,the mechanical properties of AT72 alloy are greatly improved after solution treatment at 400℃for 20 h due to solution strengthening of Al and Sn elements and precipitation strengthening of Mg_(2)Sn phases.The precipitation strengthening effect of particle Mg_(2)Sn phases is more apparent due to the decomposition of Mg_(17)Al_(12) phases.In addition,from the view of microscopic theory,the effect of Sn on mechanical properties of Mg-7Al alloy was discussed by first-principle calculation.

In-situ growth of porous Cu_(3)(BTC)_(2) on cellulose nanofibrils for ultra-low dielectric films with high flexibility

The design of flexible polymeric films with internal porous structures has received increasing attention in low dielectric applications.The highly porous metal-organic frameworks(MOFs)of[Cu_(3)(BTC)_(2)]_(n)(BTC=benzene-1,3,5-tricarboxylate)were introduced into aramid nanofibers(ANF)matrix by using carboxylated cellulose nanofibrils(CNF)as carriers to obtain strong,flexible,and ultra-low dielectric films.The well-dispersed“flowers-branch”like CNF@CuBTC through in-situ growth of CuBTC on CNF surface endowed the ANF/CNF@Cu BTC films with excellent thermal stability,mechanical integrity and low dielectric properties.Besides,the flexible dielectric films exhibited superior ultraviolet(UV)resistance,lower coefficient of thermal expansion(4.28×10^(-5)℃^(-1))and increased water contact angle(83.81°).More interestingly,the removal of guest molecules from the ANF/CNF@CuBTC films according to the vacuum heat treatment(VHT)process significantly improved their dielectric response.The specific surface areas of the composite films after VHT increased obviously,and the dielectric constant and dielectric loss tangent decreased to the expected 1.8-2.2 and 0.001-0.03 at 100 MHz,respectively.Consequently,such designable ultra-low dielectric films with high flexibility play an incredible significance in applications of microelectronics under large deformation conditions,especially in flexible/wearable devices at the arrival of 5 G era.