The friction and wear properties of NiAl, NiAl--Cr(Mo)--Hf eutectic alloy and NiAl--Al2O3--TiC composite were investigated with an MRH-5A friction and wear tester. The results showed that the wear resistance of NiAl-based alloys was directional propertional to their hardness and fracture toughness and the friction coefficient ecreased with the increasing hardness. Among the above three alloys, NiAl--Al2O3--TiC composite possessed the best friction and wear properties. The wear mass loss only one-fourth to three-fourthes of that of NiAl--Cr(Mo)--Hf eutectic alloy or one-twentieth to one-tenth of that of NiAl alloy, which was attributed to the efficient transferring stress and supporting effect of reinforcing ceramic particles. The wear process of three NiAl materials is dominated by plastic deformation, and the main wear mechanism of the three NiAl--based alloys was abrasive wear. With the increase of load, the wear surfaces exhibit orderly such wear mechanisms as distinct plastic deformation, spalling and adhesion wear. The wear mechanism played an important role in the wear rate and friction coefficent.
The cyclic oxidation behavior of the Ti--60 titanium alloy, and Ti--48Al and Ti--48Al--12Cr (atomic fraction, %) coatings at 800℃ were studied. The results showed that the Ti--60 titanium alloy showed poor oxidation resistance in the process of cyclic oxidation at 800℃, occurring with oxidation scales fall. The Ti--48Al and Ti--48Al--12Cr coatings showed good oxidation resistance at 800℃. For the Ti--48Al--12Cr coating, the weight gain is much less than that of the Ti--48Al coating, showing better cyclic oxidation resistance.
The microstructures were determined by X-ray diffraction line profile analysis. The influence of shot blasting on the matrix mechanical properties of the surface on TiB2/6351Al was investigated by using in situ tension X-ray diffraction technique. Results show that the proof stress of the matrix in the shot blasted surface had been increased by about 26% and the integral strength had been increased by 28\%. Moreover, the increment of hardness is more than 50%. The bearing stress factor of the matrix of untreated and shot peened surface is 81% and 83%, respectively. The domain size and the dislocation density of the strengthened surface are 51 nm and 3.05 X 1014m-2. The increment of mechanical properties is mainly due to the fine domain and high value of dislocation density introduced by shot blasting.
Using different 1H solid--state NMR techniques, the Cr--catalyzed ethylene--hexene copolymer with different hexene content was investigated, and the effects of comonomer content on the phase composition, molecular mobility and domain size of the copolymer were studied. The results showed that the mass fraction of crystalline phase was decreased with the hexene content increasing, while the fractions of the other two components were increased. Meanwhile, the fraction of the interface and amorphous component was increased in the NMR long period. Furthermore, we choose the variance of MI/MA , the ratio of mass fraction of interface component to the fraction of amorphous component, with temperature as the qualitative determination of the confined degree of the segment in non--crystalline region. Cr--catalyzed PE copolymer for pipe application with different duration grade was investigated. It was found that the mass fraction of rigid component decreased with the duration-grade increasing, while the fractions of the other two components increased. The same trend of the fraction in NMR long period was illustrated by the 1H spin diffusion result. The variance of MI/MA showed great correspondence to the duration grade of the materials.
Contact fatigue properties of two case hardening steels have been investigated by means of rolling contact fatigue tests with carburized specimens. Results show that most of the rolling contact fatigue specimens failed due to pitting and spalling in the carburized case. The steel microalloyed with 0.04% niobium has a lower oxygen content and fewer quantity and smaller size of oxide inclusions, which makes fatigue crack initiation more difficult. Moreover, it is also more difficult for fatigue crack propagation in the case of the niobium microalloying steel, owing to its finer grain size and higher hardness. As a result, the rolling contact fatigue life of the steel microalloyed with niobium is much higher than that of the steel without microalloying.
Six new ternary complexes of europium were synthesized with the first ligands of benzoic acid, p-methylbenzoic acid, m-chlorobenzoic acid, p-chlorobenzoic acid, p-hydroxylbenzoic acid, methoxybenzoic acid and the second ligand of butanedioic acid. Their molecular composition and structures were characterized by means of elemental analysis, EDTA titrimetric method, FT--IR and UV spectroscopies. The thermal stability properties of the title complexes were studied by thermal analysis instrument. The luminescent properties of the title complexes and their corresponding binary complexes were investigated by means of fluorescence instrument. The fluorescence spectra data show that the new ternary complexes have much higher luminescence intensity than their corresponding binary complexes.
The residual stress and micro--stress in free--standing boron--doped polycrystalline diamond films, grown by an electron--assisted hot filament chemical vapor deposition (EA--HFCVD) were analyzed by X--ray diffraction (XRD) including sin2 φ method. The results show that the residual stress is compressive. With increasing boron flow rate, the stress is gradually decreased. The micro--stress varies as tensile →compressive→ tensile in the films fabricated with increasing boron flow rate in the growth processes. The variations in the residual stress and micro--stress as a function of boron doping level are strongly dependent on the grain size, growth orientation, and appearance of twins in the boron--doped diamond films.
The effects of the aging temperature and time on precipitation behavior of 316L austenitic stainless steel were analyzed, and the volume fraction and the sizes of the precipitates were determined. By the thermodynamic calculation with the update database, the results show that the precipitated phase in 316L austenitic stainless steel was M23C6 type carbide after aging at 850℃, and the amount and size of M23C6 were increased with enhanced aging time. After aging at 650℃ for 100 h, the precipitated phase in steel was mainly composed of χ phase.
The effect of rare earth element La addition on the isothermal oxidation behavior of a Ni--Cr--W--Mo superalloy was investigated. The results showed that the oxidation resistance can be effectively improved by the addition of La element. The improving degree with the La addition from the worst to the best is 0.0%, 0.048%, 0.026%, 0.087%. For the testing alloys, 0.026% La is considered as the optimum amount. It has been found that La--riched phase precipitates with more than 0.02% La addition, and soluted La in the matrix does not increase linearly with the increasing of La addition. The amount of soluted La is considered as the main reason for the improving of oxidation resistance. Diffusion of the Cr3+ was impended by LaCrO3 segregated on the interface of oxide scale. LaCrO3 as heterogeneous nucleating of MnCr2O4, promoted the nucleation of the fine MnCr2O4 grains among the Cr2O3, forming smooth multi--oxide scale without voids, so that the bounding force between oxide scale and matrix was increased.
Al/Al2O3 cup shells with excellent mechanical properties were prepared successfully by thixoforging in pseudo-semi-solid state proposed based on the powder metallurgy technology and semi-solid metal forming process. Bend strength and fracture toughness of 37% (mass fraction) Al/Al2O3 are about 570--690 MPa and 8.5--16.8 MPa ? m1/2 respectively. It showed that the technology parameters have great influences on the mechanical properties. All results show that the composite presented is propitious to be used in more fields as the ceramic composites and high-melt point materials.
High-quality ultrananocrystalline diamond film was prepared with Ar/CH4/CO2 by using microwave plasma chemical vapor deposition (MPCVD) technology. The average size of the crystalline grains and surface roughness are about 7.480 nm and 15.72 nm, respectively. B-doped diamond thin film was synthesized by adding B2H6 into the gas resource. The results showed that within a certain limits along with the addition of B2H6, the grains size and surfaces roughness of the diamond thin films increased dramatically, and their crystallinity got better. The diamond thin film no longer had the characteristics of the ultrananocrystalline diamond film. Meanwhile, with the addition of B2H6, the diamond phase constitutes in these films increased gradually, and more obvious residual stress and better conductivity appeared at the same time.
By using high--purity tungsten powders, titanium powders and TA2 Ti sheet as the raw materials, W--10%Ti alloys were prepared by infiltration and liquid--phase sintering respectively. The density and impurity content of C, N and O in W--10\%Ti alloy were measured. The morphology, composition and microstructure were characterized. The results show that W--10\%Ti alloy prepared by infiltration has a relative density of above 94% and is mainly consisted of Ti--rich $\beta$ solid solution, while the relative density of W--Ti prepared by liquid phase sintering is about 90% and the microstructure is uniform. The W--Ti alloys prepared by both methods have low impurity contents. The formation mechanism of W--10\%Ti alloy by liquid phase sintering was discussed as well.
The sirolimus--releasing PLA--PTMC coating was successfully prepared on the biodegradable AZ31B magnesium alloy coronary stents. The surface morphology, degradability, biocompatibility and drug release characteristic of the coating were also evaluated. The results indicated that PLA--PTMC used as the drug elution coating showed good flexibility with smooth and uniform surface, the degradation period was over one month, and the biocompatibility was excellent. The drug--loaded coating had releasing function of sirolimus and the releasing time was more than one month, which could effectively inhibit the restenosis during the period of intima hypertrophy. The sirolimus--releasing PLA--PTMC coating showed potential to be used as a new type of coronary stent coating.
The effect of “quenching--partitioning--tempering”(Q--P--T) process on three--body impact--abrasion of 20Si2Ni3 steel was investigated. The results show that as increasing of the impact energy from 0.5 J to 3.5 J, the mass loss of the samples increases firstly and then decreases, and reaches maximum value at the impact energy of 2.5 J. The mass loss of the samples treated by Q--P--T is lower than those treated by Q--T. Major abrasion behavior is transition from cut to fatigue, and the thickness of the surface work--hardening for the samples treated by Q--P--T is much larger than that of Q--T treated. It is reasonable to propose that the better resistance in impact abrasive for the samples treated by Q--P--T process arises from high--toughness, work--hardening of the alloy matrix, the phase and deformation transformation strengthening of the retained austenite during abrasing.
A kind of composite adhesive of the ionic liquid/fir powder/phenol-formaldehyde (PF) was prepared. Effects of the fir powder and ionic liquid on properties of the composite adhesive were investigated. Curing temperature, chemical structure and thermal stability of the composite adhesive were analyzed by DSC, FTIR and TGA, respectively. The results showed that the fir powder could decrease free formaldehyde effectively of the composite adhesive and the ionic liquid could increase the adhesive properties greatly. Free formaldehyde in the composite adhesive decreased from 1.76% to 0.24% compared to conventional PF adhesive, tensile shear strength increased from 2.16 MPa to 5.39 MPa when the mass ratio of the ionic liquid to fir powder was 10 : 1, and the cured composite adhesive had no crack and was also comparatively transparent. TGA indicated that initial thermal decomposition temperature of the composite adhesive was increased, but the content of residual carbon was decreased. Capture of the fir powder after dissolved in the ionic liquid for formaldehyde and contribution of the ionic liquid to the adhesive properties had been discussed.
The evolution of a single dendrite growth and the morphology of multi–dendrite during isothermal solidification of Fe–0.5%C alloy are simulated using phase field method. The effects of supercooling, anisotropy of crystal, interface thickness and crystal orientation as well as the noise on the dendritic morphology are studied. The results illustrate that the morphology of the dendrite is composed of the primary and secondary arms. The process of the dendrite growth and the competition between the dendrite arms are reproduced during solidification. The solute enrichment and the dendrite segregation occur during solidification. The primary arms have the lowest concentration, but the regions between the arms have the highest concentration because of the build–up of solute. With the increment of supercooling, the dendrite grows quickly and the branches are developed. The interface thickness impacts the growth velocity of dendrite. The anisotropy of the crystal exerts an influence on the dendritic morphology. The dendrite grows preferentially when the crystal orientation is consistent with the coordinate axis. The noise leads to the development of the dendritic branches.
To reducing surface roughness, TiO2 film with different lay numbers was coated on the TiO2 film containing SrFe12O19 powder on the surface of NiTi alloy and 316L stainless steel with sol-gel method. The surface roughness of these films were investigated by SEM and surface roughometer, and the dynamic clotting time and hemolysis rate of these different roughness micromagnetic field surfaces were tested. The results showed that the blood compatibility on the micromagnetic field surface with low roughness is better, that is, smoother micromagnetic field surface can be used to further improve the blood compatibility of the materials.
NiMnGaSi alloy powder was prepared by diffusion-reduction method and then bonded and shaped a cuboid. The magnetic properties of the sample show that a martensitic transformation starts at 308 K and the Curie temperature is 358 K. The NiMnGaSi alloy shows a 0.56% giant strain at room temperature under a magnetic field of 0.7 T.
Tungsten oxide thin films were prepared on 3Cr13 martensite stainless steel, and then the films were sulfurized in a quart heating-furnace with quantitative sulfur at 200, 400, 600 and 800 for 4 h. The effect of the sulfurizing temperature on frictional behavior of the tungsten disulfide thin film was studied. The results showed that the sulfurizing temperatures influenced surface topography and crystallization obviously. But the influence on chemical constitution was not obvious. The frictional behaviour of the stainless steel basal plant subjected to be sulfurized was improved. With the increasing of the sulfurizing temperatures, the fiction coefficient of the films reduced and the fiction coefficient was also influenced by the testing environment and conditions.
