Guangze Tang

Microstructure and variable emittance property of annealed La-Sr-Mn-O films

Abstract The La-Sr-Mn-O films were deposited on Si(100) substrates by DC magnetron sputtering and followed by air annealing at 973 K for 1 h. The microstructure and temperature dependence of total hemispherical emittance (ɛ H ) of the annealed La-Sr-Mn-O films prepared at various processing parameters were investigated. The results indicated the films deposited at lower sputtering pressure and lower O 2 /(O 2 +Ar) volume proportion ( R O ) were present in rhombohedral perovskite structure and the length of Mn-O bond was shorter. The metal-insulator transition temperature ( T MI ) was higher. All of the annealed films showed the unique feature of variable emittance based on metal-insulator transition. The films showed low emittance at low temperature but high emittance at high temperature. Moreover, the ɛ H significantly changed in the vicinity of T MI . The variability of total hemispherical emittance (Δɛ) and the temperature range with obvious emittance change could be adjusted by changing the processing parameters. The Δɛ could be 0.45 and Δɛ/ɛ 355 (ɛ 355 is the ɛ H at 355K) exceeded 50% for the annealed La-Sr-Mn-O films. Therefore, the annealed La-Sr-Mn-O films showed much potential for thermal control applications as smart thermochromic variable emittance materials.

Composition and corrosion resistance of cerium conversion films on 2195Al-Li alloy

Abstract The Ce conversion films on 2195Al-Li alloy without and with post-treatment were studied and the corrosion resistance was evaluated as well. The surface morphology was observed by scanning electron microscopy (SEM), and the chemical composition was characterized by X-ray photoelectron spectroscopy (XPS). The corrosion behaviors of 2195Al-Li alloy and conversion coating were assessed by means of potentiodynamic polarization curves. The experimental results indicated that after post-treatment the surface quality was improved significantly. According to XPS, the conversion coating after post-treatment was mainly composed of CeO 2 , Ce 2 O 3 , Ce-OH and a little MoO 3 and MoO 2 . The results of potentiodynamic polarization curves revealed that the conversion coating with post-treatment possessed better corrosion resistance than bare alloy and Ce conversion coating without post-treatment.

Nanoscratch behaviors of La0.7Sr0.3MnO3+δ thin films

Abstract The nanoscratch behaviors of La 0.7 Sr 0.3 MnO 3+δ films, which were deposited with ratio of O 2 /(O 2 +Ar), ranging from 4.4% to 45.6%, by DC magnetron sputter, were investigated by a nanoindentation technique. The results indicated that the friction coefficient between the films and the diamond tip depended on the loading critical load. The friction coefficient was about 0.08–0.12 when the loading normal load was less than the loading critical load. The films displayed excellent elastic recovery after unloading. When the loading load was larger than the loading critical load, plastic deformation and ploughing appeared for the films. The friction coefficient was about 0.43 when the film was damaged completely. The suitable decrease in ratio of O 2 /(O 2 +Ar) could improve the nanoscratch resistance of the films. The film deposited with O 2 /(O 2 +Ar)=25% possessed better scratch resistance due to good elastic recovery, high nanohardness, and critical load. The loading critical load of the film was larger than 80 mN.

Study on Properties of M50 Steel Implanted With Nitrogen by Plasma-Based Ion Implantation at Elevated Temperatures

M50 steel was implanted with nitrogen at elevated temperatures ranging from 260 degC to 420 degC using plasma-based ion implantation. The effect of implantation temperature on surface microstructure, hardness, and wear resistance was investigated. It is observed that nitrogen penetrates very deeply from the surface as a result of implantation and thermal diffusion at elevated temperatures. The amount of nitrides and their distribution depth as well as the hardness and the wear resistance in the surface layer increase with the processing temperature. As the implantation temperature increases, the wear mechanism changes from adhesive wear to abrasive wear

Influence of Grinding Particle Size on Structure and Electrical Properties of La0.67Sr0.33MnO3−δ Compound

In this article, the influences of grinding particle size on the structure and electrical transport properties of La0.67Sr0.33MnO3−δ compound have been investigated. The compound was prepared by gel combustion process followed by grinding for different duration time. It was found that the lattice parameters, unit-cell volume, strain, oxygen deficiency, and temperature dependence of resistivity ρ–T increase with decreasing particle size. The ρ–T growth can be explained by the increasing contribution of the grain boundary effect, strain, and even oxygen deficiency. The electrical transport mechanism over the whole temperature range of 100–400 K was thoroughly described by applying the phase separation model around the phase transition temperature TP. This model was subsequently employed to calculate the ρ–T at high temperature up to 1000 K. The result showed there was a second phase transition at a typical temperature T*>TP, which could be attributed to the relaxation of small polarons to large ones. This relaxation occurred at lower temperatures when the particle size decreased. It might be due to the decrease in conduction bandwidth caused by the defects arisen during the grinding.

Boundary Tribological Behaviors of Untreated and Surface-Modified M50 Steel Lubricated by Fuel JP-10

ABSTRACT To explore the possibility of using advanced surface engineering techniques (ASETs) to solve the wear problems caused by the poor lubricity of pure, low-viscosity aviation fuel JP-10, polished M50 bearing steel sample surfaces were treated with nitrogen ion implantation, TiAlN coating deposition, and Ta coating deposition followed by high current pulsed electron beam (HCPEB) irradiation, respectively. Boundary tribological behaviors of these ASET-treated and untreated steel samples sliding in pure JP-10 against a Si3N4 ball (ball-on-disc model) were investigated under 2.0 GPa in the atmosphere and the friction tests indicated that significant, reductions, although to different extents, in friction and wear were achieved by these modified surfaces. Simultaneously considering the tribological performance and potential pollution caused by wear debris to JP-10, HCPEB-treated Ta coating with a lowest average friction coefficient of 0.11 and a specific wear rate of around zero was the fittest to offset the inadequate lubricity of JP-10 itself under the laboratory condition.

In situ observation on microstructural development of high-speed steel during carbon partitioning process

ABSTRACT Quenching–partitioning–tempering (Q–P–T) process was applied to treat high-speed steel. Microstructural development and properties were studied using high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy, X-ray diffraction and a drop hammer impact toughness tester. The results of impact toughness test showed that the impact absorption energy increased to 16.2–20.1 J along the Q–P–T process, namely 56–93% higher than that of traditional Q–T approach (10.4 J). The results of in situ HRTEM showed that the interface of martensite/austenite (α/γ) migrated from martensite towards austenite with the increase of holding time, which led to a reduction of retained austenite. One of the migration planes was (110)α/(111)γ. The cementite precipitation and slight decomposition of retained austenite were observed during carbon partitioning process.

Equilibrium concentration of carbon in high-carbon high-alloy steel during carbon partitioning process

Carbon partitioning was applied to treat high-carbon high-alloy steel. Equilibrium concentration of carbon was studied by constrained carbon equilibrium (CCE) criterion and modified model (CCEA) which took the effect of alloying elements on the carbon activity into account. The results of X-ray diffraction (XRD) analyses showed that the carbon concentration of retained austenite increased first and then decreased with the holding time, and the approximate equilibrium concentration of carbon was closer to the predicted results by CCEA. Simultaneously, the results of XRD analyses represented that the structure of martensite in quenched and partitioned steel was body-centred tetragonal. Carbide precipitation was observed in specimens during the partitioning step by scanning electron microscope and high-resolution transmission electron microscopy.

Effect of Implantation Sequence on Tribological Behavior of GCr15 Steel by PBII

In the present work, the effect of implantation sequence on tribological behavior of GCr15 steel treated by plasma-based ion implantation of carbon and nitrogen has been investigated. The treated GCr15 steels were characterized for microstructure and abrasive wear performance through combination of Raman spectroscopy, nano-indentation, and wear tests. Raman spectroscopy indicated that diamond-like carbon (DLC) films were formed after implantation of carbon with or without implantation of nitrogen, and the implantation of nitrogen after the implantation of carbon destroyed the graphite structure of the DLC films. The nano-indentation and wear tests showed that nanohardness as well as wear resistance of the GCr15 steel treated with the implantation sequence of nitrogen-carbon was better than those with the implantation sequence of carbon-nitrogen. Meanwhile, the properties were improved with increasing of carbon ion fluence.

Self-Lubricated Modification for Silicon Nitride Ceramic Ball Surface

Some thin films were prepared as solid lubricants on the surfaces of silicon nitride ceramic disk and ball. DLC film about 500–800 nm thickness was deposited on the ceramic surfaces using ion implantation and deposition technology. The surface roundness measure results, as well as 80 to 90 nm, showed that DLC film was shaped uniformly on the ceramic ball surfaces. The ball-on-disk tests showed DLC coating on silicon nitride surfaces could lead the friction coefficient to about 0.1 and endure about 7h at 1.5GPa and 30 mm/s. Ball milling technology was employed to prepare MoS2 film on the ceramic ball surfaces. The film thickness and tribological test results showed that the thin MoS2 film on the ball surfaces, which hardly changed the surface roughness, also improved their wear behaviors.Copyright