Effect of(Cr,V)_(2)(C,N)on the Microstructure and Mechanical Properties of WC-10Co Cemented Carbides

WC-10Co cemented carbides with finer WC and narrower grain size distributions are produced by using(Cr,V)_(2)(C,N)as grain growth inhibitors.As a result,with the increase of(Cr_(0.9),V_(0.1))_(2)(C,N)and(V_(0.9),Cr_(0.1))_(2)(C,N),the grains size of WC and mean free path of Co phase decrease,and adjacency of WC increases.Refinement and homogenization of grains enhance the transverse rupture strength(TRS)and the hardness.Meanwhile,the deflection and bridging of cracks keep the fracture toughness at a respectable level.The WC-10Co-0.6(Cr_(0.9),V_(0.1))_(2)(C,N)-0.025(V_(0.9),Cr_(0.1))_(2)(C,N)cemented carbides exhibit excellent comprehensive mechanical properties with the TRS of 4602.6 MPa,hardness of 1835 kg/mm^(2),and fracture toughness of 10.39 MPa·m^(1/2),respectively.However,the large pores are caused by excess N larger than 0.03 wt%and deteriorates the mechanical properties.We provide a new approach to WC-Co cemented carbides preparation with a narrow grain size distribution by adding novel grain growth inhibitors.

Effect of Sintering Temperature on the Microstructure and Mechanical Properties of Nanocrystalline Cemented Carbide

WC-Co nanocrystalline nitrogen-containing cemented carbides were prepared by vacuum sintering and low pressure sintering.The sintering processes of Cr_(2)(C,N)doped nano WC-Co powders were studied by using thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC).The effect of sintering temperature on the microstructure and mechanical properties of nanocrystalline cemented carbide was studied by scanning electron microscope(SEM),high resolution transmission electron microscope(HRTEM)and mechanical property test.The results showed that the nano WC grains began to grow in the solid phase sintering stage.A high-performance nano-nitrogen-containing cemented carbide with uniform microstructure and good interfacial bonding can be obtained by increasing the sintering temperature to 1380℃.It has a transverse rupture strength(TRS)of 5057 MPa and a hardness of 1956 HV30.

Improvement of the microstructure and magnetic properties of(La,Ce)-Fe-B nanocrystalline ribbons

The obstacles of inferior microstructure and poor magnetic properties of(La,Ce)-Fe-B type magnets stand in the way of expanding their applications.In this work,(La,Ce)-Fe-B melt-spun ribbons were prepared with different La/Ce ratios and rare earth contents.The microstructure and magnetic properties of these ribbons were investigated.With the La/Ce ratio increased,the fraction of the CeFe_(2)phase decreased and the β-La phase segregated among matrix grains,which deteriorated the coercivity of the ribbons.Reducing the rare earth content effectively suppressed the β-La phase and improved the proportion of the matrix phase in the ribbons.Here,the optimal alloy composite(La_(15)Ce_(85))_(14)Fe_(80)B_(6) has been obtained with modified microstructure and inhibited secondary phases.Good ribbon performance was tested,with H_(cj)=4.51 kOe,B_(r)=6.29 kG and(BH)_(max)=6.81 MGOe.

The effect of high-temperature annealing on LaFe_(11.5)Si_(1.5) and the magneto-caloric properties of La_(1-x)Ce_xFe_(11.5)Si_(1.5) compounds

The powder X-ray diffraction patterns of LaFell.sSil.5 compounds annealed at different high temperatures from 1323 K （5 h） to 1623 K （2 h） show that a large amount of 1：13 phase begins to form in LaFell.sSiL5 compound annealed at 1423 K （5 h）. In the temperature range from 1423 to 1523 K, ^-Fe and LaFeSi phases rapidly decrease to form 1：13 phase. LaFeSi phase is rarely observed, and the most amount of 1：13 phase is obtained in the compound annealed at 1523 K （5 h）. With the annealing temperature increasing to 1573 and 1623 K, LaFeSi is detected again in the LaFell.sSil.s compound. According to the results of annealing at different high-temperatures, the Lal-xCexFelt.sSit.5 compounds are annealed at high temperatures of 1373 K （2 h） ＋ 1523 K （5 h）. The main phase is NaZn13-type phase, and the impurity is a small amount of et-Fe in Lal-xCexFexx.sSil.5 compounds with 0 〈 x 〈 0.35, and there is a large amount of CeaFe17 phase in Lao.sCeo.sFela.sSil.s. It indicates that the substitution of cerium atoms for La in LaFelLsSil.5 compounds has limit. At the same time, the substitution of Ce for La has large effect on magnetocaloric properties. With increasing Ce content from x = 0 to x = 0.35, the Curie temperature decreases linearly from 196 to 168 K, the magnetic entropy change increases from 16.5 to 57.3 J-kg-kK-1 in a low magnetic field change of 0-2 T, and the thermal hysteresis also increases from 3 K to 8 K.

Relationship of microstructure transformation and hardening behavior of type 17-4 PH stainless steel

The relationship between the microstructure transformation of type 17-4 PH stainless steel and the aging hardening behavior was investigated. The results showed that, when 17-4 PH stainless steel aging at 595℃, the bulk hardness of samples attains its peak value （42.5 HRC） for about 20 min, and then decreases at all time. TEM revealed the microstructure corresponding with peak hardness is that the fine spheroid-shape copper with the fcc crystal structure and the fiber-shape secondary carbide M23C6 precipitated from the lath martensite matrix. Both precipitations of copper and M23C6 are the reasons for strengthening of the alloy at this temperature. With the extension of holding time at this temperature, the copper and secondary carbide grow and lose the coherent relationship with the matrix, so the bulk hardness of samples decreases.

Effects of Nitrogen Atmosphere on Microstructure and Mechanical Properties of Ti(C_(0.5)N_(0.5))-based Cermets

The traditional low-pressure sintering was optimized for the preparation of Ti(C_(0.5)N_(0.5))-WC-Mo_2 C-TaC-Co-Ni cermets. Nitrogen was introduced into sintering system during different stages and with different pressures. The morphology and mechanical properties of cermets were investigated by scanning electron microscopy(SEM), X-ray diffraction(XRD), and measurements of transverse rupture strength(TRS), Vickers-hardness(HV) and fracture toughness(K_(IC)). The degree of denitrification is directly related to the amount of η phase. When nitrogen is introduced into the sintering system, the amount of observed η phase decreases. When nitrogen is introduced during solid-state sintering with appropriate pressure, the core-rim structure is well developed. And TRS and hardness get enhanced while toughness tends to be deteriorated with the nitrogen pressure increasing. When nitrogen is introduced after the sintering temperature reaches 1 350 ℃ or at higher pressures, the volume fraction of η phase increases. Sintered with a nitrogen pressure of 1.0 kPa during 1 200-1 350 ℃, the bulk materials possess enhanced mechanical properties, in which the TRS, HV, and K_(IC) are 1 966 MPa, 1 583 MPa, and 9.08 MPa·m^(1/2), respectively.

Effects of solidification rate and excessive Fe on phase formation and magnetoclaoric properties of LaFe_(11.6x)Si_(1.4)

The effects of solidification rate and excessive Fe on phase formation and magnetocaloric properties of LaFe11.6xSi1.4(x=1.1,1.2)were investigated by XRD,SEM and VSM measurements.The XRD results show that the amount of LaFeSi phase in the as-cast melt-spun ribbons prepared by a copper wheel at a speed of10m/s is less than that in the as-cast arc melting buttons with the same x values.The annealed melt-spun ribbons contain smaller amount of La(Fe,Si)13(1:13)phase than the corresponding annealed arc melting buttons.Although the melt-spun sample has finer crystalline grains ofα-Fe,as indicated by SEM analysis,its crystalline size has not reached nano-scale.Therefore,the magnetic exchange-coupling between1:13phase andα-Fe phase has not been observed in melt-spun ribbons.Further,the maximum negative magnetic entropy change(?SMax)and relative cooling power(RCP)of annealed melt-spun ribbons under a field change of0?2T are weaker than those of the corresponding annealed arc melting buttons.

Microstructures,mechanical properties and compressive creep behaviors of as-cast Mg-5%Sn-(0-1.0)%Pb alloys

The microstructures, tensile properties and compressive creep behaviors of Mg-5%Sn-（0-1.0）%Pb （mass fraction） alloys were studied. The microstructures of the Mg-Sn-Pb alloys consist of dendritic a-Mg and Mg2Sn phase. The addition of Pb can refine the size of Mg2Sn phase and grain size, reduce the amount of Mg2Sn phase at grain or inter-dendrite boundaries and change the distribution of Mg2Sn phase. Pb exists in the Mg2Sn phase or dissolves in a-Mg matrix. The mechanical properties of the tested alloys at room temperature are improved with the addition of Pb. When the Pb content is over 0.5%, the mechanical properties are decreased gradually. The Mg-5%Sn-0.5%Pb shows the best ultimate tensile strength and elongation, 174 MPa and 14.3%, respectively. However, the compressive creep resistance of the Mg-Sn-Pb alloys is much lower than that of the Mg-Sn binary alloy at 175℃ with applied load of 55 MPa, which means that Pb has negative effects on the compressive creep resistance of the as-cast Mg-Sn alloys.

Microstructure and Properties of Mg-10% Al-(0～3% )Di Alloys

The effects of didymium(Nd : Pr = 3 : 1 )on the microstructure and mechanical properties of Mg-10%A1 alloy were studied with the additions of 0~3%Di. The small block-like Al2(Nd,Pr) phase appears in 1%Di alloy, the blocklike Al2(Nd,Pr) and needle-like Al11(Nd,Pr)3 phases appear synchronously in 2%Di and 3%Di alloys, while the network of (Mg17Al12)βphase is broken up. The tensile properties can be improved with the addition of didymium. When the addition of didymium in Mg-10%A1 alloy reaches 2% , the alloy exhibits the best combination of strength and ductility, but the strength and ductility drop at the addition of 3% Di due to the obvious increase of the size and quantity of the needle-like Al11(Nd,Pr)3 phase.

Microstructure,tensile properties and compressive creep resistance of Mg-(5-8.5)%Sn-2%La alloys

The microstructure,tensile properties and compressive creep resistance of permanent-mould cast Mg-(5-8.5)%Sn-2%La (mass fraction) alloys were investigated.The results show that Mg-(5-8.5)%Sn-2%La alloys are all composed ofα-Mg phase, Mg_2Sn and Mg-La-Sn compounds.Compared with those of Mg-5%Sn binary alloy,the grain size and the content of Mg_2Sn compound in Mg-5%Sn-2%La alloy are decreased.With the increase of Sn content in Mg-(5-8.5)%Sn-2%La alloys,the content of Mg_2Sn compound increases,while that of Mg-Sn-La compound changes little.In addition,the investigation suggests that the thermally stable Mg-Sn-La and Mg2Sn compounds can improve the tensile properties and compressive creep resistance of the alloys.

Fabrication, characterization and electrochemical properties of porous palladium bulk samples with high porosity and hierarchical pore structure

In the present study,porous bulk palladium samples were prepared by sodium chloride salt powder spacer incorporation and removal combined with dealloying.The obtained porous Pd bulks were characterized by X‐ray diffraction,field‐emission scanning electron microscopy and N2adsorption isotherm measurements.The prepared porous Pd bulk samples showed a hierarchical pore structure,a high porosity of^88%,a high surface area of^54m2/g,and a compression strength of^0.5MPa.Electrochemical measurements were performed to evaluate the electrocatalytic properties of the porous Pd bulk samples,revealing their effectiveness for ethanol oxidation.

Mechanical Properties and Uniformity of Nanocrystalline Diamond Coating Deposited Around a Sphere by MPCVD

Nanocrystalline diamond coatings were deposited by MPCVD on the spheres used for a ball bearing.The nanocrystalline coatings with a grain size of 50 nm were confirmed by the surface morphology and composition analysis.The hardness of the coating is 20-40 GPa tested by nanoindentation,which is higher than that of tungsten carbide and silicon nitride substrates.The coating around the sphere observed from the Micro CT images is uniform with a thickness of 12 μm.

Frequency Up-conversion Luminescence Properties and Mechanism of Tm^(3+) /Er^(3+)/Yb^(3+) Co-doped Oxyfluorogermanate Glasses

Oxyfluoride glasses were developed with composition 60GeO 2 ·10AlF 3 ·25BaF 2 ·（1.95-x）GdF 3 · 3YbF 3 ·0.05TmF 3 ·xErF 3 （x=0.02,0.05,0.08,0.11,0.14,0.17）in mole percent.Intense blue（476 nm）,green（524 and 546 nm）and red（658 nm）emissions which identified from the 1G 4 →3H 6 transition of Tm3＋and the（2H 11/2 ,4S 3/2 ）→4I 15/2 ,4F 9/2 →4I 15/2 transitions of Er3＋,respectively,were simultaneously observed under 980 nm excitation at room temperature.The results show that multicolor luminescence including white light can be adjustably tuned by changing doping concentrations of Er3＋ion or the excitation power.In addition,the energy transfer processes among Tm3＋,Er3＋and Yb3＋ions,and up-conversion mechanisms are discussed.

Effect of Aluminum Coating on Corrosion and Heat Transfer Performance of Magnetic Refrigerant Gadolinium

The surface of gadolinium was covered with a layer of Al film(10-15 μm) by hot-press.Corrosion resistance, thermal conductivity and diffusivity of the composites were studied. As a result,temperature and pressure are the main factors that influence the combination of Gd and Al, and the effect of pressure is especially obvious. When the pressure exceeds 700 MPa, the binding force reaches 9 MPa. After coating, corrosion resistance of the composites is significantly improved, Corrosion rate is significantly reduced and mass loss reduced to one-tenth of pure Gd after 15 days. The current density decreases by an order of magnitude and corrosion potential increases by 0.3 V. The thermal conductivity of the composites is 11.12 W·m^-1·K^-1. Due to good thermal diffusion coefficient of aluminum, the magnetic work piece coated with Al film might show better heat transfer performance.

Structures and Stability of Metal Amidoboranes (MAB): Density Functional Calculations

Molecule geometry structures, frequencies, and energetic stabilities of ammonia borane （AB, NH3BH3 ） and metal amidoboranes （MAB, MNH2BH3）, formed by substituting H atom in AB with one of main group metal atoms, have been investigated by density-functional theory and optimized at the B3LYP levels with 6-311G＋＋ （3dr, 3pd） basic set. Their structural parameters and infrared spectrum characteristic peaks have been predicted, which should be the criterion of a successfully synthesized material. Several parameters such as binding energies, vibrational frequencies, and the energy gaps between the HOMO and the LUMO have been adopted to characterize and evaluate their structure stabilities. It is also found that the binding energies and HOMO-LUMO energy gaps of the MAB obviously change with the substitution of the atoms. MgAB has the lowest binding energy and is easier to decompose than any other substitutional structures under same conditions, while CaAB has the highest chemical activity.

Sliding wear behaviour of Fe/316L/430-Ti(C,N)composites prepared via spark plasma sintering and subsequent heat treatment

A series of novel steel-Ti(C,N)composites was fabricated by spark plasma sintering(SPS)and subsequent heat treatment.The hardness,indentation fracture resistance,and wear behaviour of the steel-Ti(C,N)composites were compared with those of the unreinforced samples,and their potentials were assessed by comparison with traditional cermet/hardmetal systems.The results showed that with the addi-tion of 20wt%Ti(C,N),the wear rates of the newly examined composites reduced by a factor of about 2 to 4 and were comparable to those of cermets and hardmetals.The martensitic transformation of the steel matrix and the formation of in situ carbides induced by heat treatment en-hanced the wear resistance.Although the presence of excessive in situ carbides improved the hardness,the low indentation fracture resistance(IFR)value resulted in brittle fracture,which in turn resulted in poor wear property.Moreover,the operative wear mechanisms were investig-ated.This study provides a practical and cost-effective approach to prepare steel-Ti(C,N)composites as potential wear-resistant materials.

Two-step Synthesis of TiC_(0.7)N_(0.3)@WC-MoC_2 Core-shell Microspheres and Fabrication of TiC_(0.7)N_(0.3)@WC-MoC_2-based Cermets by SPS

The precursor with TiC0.7N0.3@WO3-MO3 microspheres were prepared by a novel method from the WO3-MoO3 sol dipping. Subsequently, TiC0.7N0.3@WC-MoC2 core-shell structural microspheres were successfully obtained by carburizing the precursor at 900 °C in a flowing mixture of CH4 （20 ml·min-1） and H2 （200 ml·min-1） for 2 h. Then TiC0.7N0.3@WC-MoC2-15Co cermets were prepared utilizing the core-shell powders by spark plasma sintering （SPS）. Powders of the precursors with TiC0.7N0.3@WO3-MO3 microspheres, TiC0.7N0.3@WC-MoC2 microspheres and TiC0.7N0.3@WC-MoC2-15Co cermets were characterized by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray diffraction （XRD）. The obtained TiC0.7N0.3@WC-MoC2 microspheres have a dense WC-MoC2 coatings shell. The thickness of the shell could be easily controlled by adjusting the number of sol dipping cycles. It was found that the TiC0.7N0.3@WC-MoC2 microspheres were more beneficial to fabricate the ＂core-rim＂ structures by SPS.

Magnetic Transition and Magnetic Entropy Change of Gd_5Si_(1.75)Ge_(1.75)Sn_(0.5)

Gd5Si1.75 Ge1.75 Sn0.5 was prepared by arc melting method. The crystal structure and magnetic properties were investigated by XRD and VSM, respectively. The magnetization of the Gd5Si1.75 Ge1.75 Sn0.5 alloy changes abruptly near its corresponding Curie temperature 269 K, possesses a typical first which means that the alloy order phase transition. The Gd5Si1.75Ge1.75 Sn0.5 adopts in Gd5Si2Ge2-type monoclinic structure at room temperature, the maximal magnetic entropy change at a magnetic field change of 1.8 T is as large as 16.7 J·kg^-1·K^-1, exceeding that of Gd about two times and is a little larger than that of Gd5Si2Ge2.

Physicochemical Characteristics of Soil Moisture and Their Effects on the Corrosion Behavior of Buried Mild Steel in Calabar Metropolis, Nigeria

Soil moisture collected from three locations, namely University of Calabar (UNICAL), Calabar municipal solid waste dumpsite (MSWD) and a mechanic workshop (MW) all within Calabar metropolis, Nigeria, were analyzed quarterly in a one year study at different depths (0.5 m and 1 m) for some physicochemical parameters. UV-visible spectrophotometer, titration and atomic absorption spectrophotometer (AAS) were the employed analytical techniques. With the exception of chloride, all other parameters showed higher values with depth. Higher values for the analyzed parameters were generally reported for MSWD and this was largely the result of the presence of a variety of contaminants in this location. Microbial analysis of soil samples from the locations revealed the presence of SRB in MW, which could have possibly influenced the soil moisture chemistry of the location. Corrosion rate was calculated from weight loss measurements and the quarterly results were all for follow the trend: UNICAL < MW < MSWD. At the end of the 4th quarter, the corrosion rates at 0.5 m depth were 0.0057, 0.0070, and 0.0101 mm/hour for UNICAL, MW, and MSWD, respectively, while their corresponding values at 1 m depth were 0.0087, 0.0114, and 0.0128 μm/hour. The values were shown to increase with depth. R-mode factor analysis identified some important factors which could have been responsible for the variation in the chemistry of the soil moisture.

Biological oyster shell waste enhances polyphenylene sulfide composites and endows them with antibacterial properties

To date,there is no research that deals with biological waste as fillers in polyphenylene sulfide(PPS).In this study,oyster shells were recycled and treated to prepare thermally-treated oyster shells(TOS),which were used as PPS fillers to make new bio-based antibacterial composite materials.The effect of varying the content of TOS was studied by means of structure and performance characterization.PPS/TOS composites were demonstrated to have an antibacterial effect on the growth of E coli and S.aureus.Qualitative analysis showed that when the TOS content was≥30%and 40%,the composite materials had an apparent inhibition zone.Quantitative analysis showed that the antibacterial activity increased with the TOS content.Fourier transform infrared spectroscopy indicated the formation of hydrogen bonds between the molecular chains of TOS and PPS and the occurrence of a coordination reaction.At 10%TOS,the composite tensile strength reached a maximum value of 72.5 MPa,which is 9.65%higher than that of pure PPS.The trend of bending properties is the same as that of tensile properties,showing that the maximum property was reached for the composite with 10%TOS.At the same time,the crystallinity and contact angle were the highest,and the permeability coefficient was the lowest.The fatigue test results indicated that for the composite with 10%TOS,the tensile strength was 23%lower than static tensile strength,and the yield strength was 10%lower than the static yield strength.The results of the study showed that TOS not only could reduce the cost of PPS,but also could impart antibacterial properties and enhance the mechanical and,barrier properties,the thermostability,as well as the crystallinity.