Microstructure and properties of gradient cemented carbide with Nano-TiN

Gradient cemented carbides with nano-TiN were prepared by the common powder metallurgical procedure. The formation of gradient zone and the microstructure, properties of the alloys were investigated using scanning electron microscope（SEM）, energy dispersive spectroscopy（EDS） and other performance testing apparatus. Moreover, the effect of nano-TiN on the gradient cemented carbide was studied. It is found that gradient zone width increases slightly with nano-TiN introduction. Both cobalt and titanium concentrations reach the maximum near the gradient border. Tungsten concentration shows fluctuation from the surface to the bulk. （Ti ,W）C phase grains are refined for nitrogen introduction. Core-rim structure has been observed under the SEM back-scattered mode. The core appears as dark due to more titanium in it and the rim with more tungsten appears as grey. In addition, the hardness and transverse rupture strength of gradient cemented carbide are enhanced with nano-TiN introduced.     

Influences of Carbon Content on the Properties and Mierostrueture of Ultrafine WC-10Co Cemented Carbide

WC-10Co nanocrystalline composite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing （HIP）. Influences of carbon content on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that the relative density of the ultrafine WC-10Co cemented carbides can reach 99.72%, and the transverse rupture strength （TRS） was higher than 3 890 MPa, Rockwell A hardness （HRA） was higher than 92.5, the average grain size was less than 460 nm, when carbon content in nanocrystalline composite powder was 5.54wt% and the ball-milled time was 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and homogeneous microstructure was obtained.     

Loose Sand Cemented by Microbial Cementitious Material:Composition,Microstructure and Mechanical Properties

Through the influence of the dosage of culture solution and calcium source on hardness and compressive strength of samples,the formulation of microbial cementitious materials was optimized and defined.The influence of temperature on composition,microstructure and mechanical properties of loose sand cemented by microbial cementitious material was compared and analyzed systematically.With the increase of temperature,the performance of loose sand was improved remarkably.Calcite with cementitious properties could be induced at higher temperatures,but not at lower temperatures.When the temperature was 30 ℃,loose sand cemented by microbial cementitious material had more calcite and more dense structure.Moreover,hardness and compressive strength were also superior.The wind tunnel test showed that the wind erosion resistance was improved obviously and the mass loss was lower at high temperature.Engineering properties of loose sand cemented by microbial cementitious material was measured integrally.Through comparative analysis,engineering properties of loose sand were basically unchanged,and there was no negative effect on the later period use of sand.     

Effects of cryogenic treatment on mechanical properties of extruded Mg-Gd-Y-Zr（Mn） alloys

The influence of cryogenic treatment on the mechanical properties of the extruded Mg-Gd-Y-Zr（Mn） alloys was investigated by the tensile tests, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, and energy dispersive X-ray spectroscopy （EDS）. The results show that the mechanical properties of both alloys are improved greatly during the in situ tensile test by soaking the samples in liquid nitrogen for 10 min. The ultimate tensile strength, yield tensile strength and elongation of cryogenic treated magnesium alloy added with zirconium or manganese are largely elevated. And remarkable microstructure change is observed in both alloys by cryogenic treatment. There are a large number of twins, rod-like, tree-like and chrysanthemum-like precipitated phases in the microstructures and the fracture surfaces exhibit the characteristics of ductile rupture when they are observed at room temperature.     

Formation mechanism of gradient-distributed particles and their effects on grain structure in 01420 Al-Li alloy

Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization. The thermo-mechanically processed sheets were observed to contain layers of different microstructures along the thickness. The precipitate behavior of the second phase particles and their effects on the distribution of dislocations and layered recrystallized grain structure were analyzed by optical microscopy（OM）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM） and X-ray diffractometry（XRD）. The formation mechanism of the gradient particles was discussed. The results show that after aging, a gradient distribution of large particles along the thickness is observed, the particles in the surface layer（SL） are distributed homogeneously, whereas those in the center layer（CL） are mainly distributed parallel to the rolling direction, and the volume fraction of the particles in the SL is higher than that in the CL. Subsequent rolling in the presence of layer-distributed particles results in a corresponding homogeneous distribution of highly strained regions in the SL and a banded distribution of them in CL, which is the main reason for the formation of layered grain structure along the thickness in the sheets.     

Mierostrueture and Properties of Coating from Cemented Carbide on Surface of Hl3 Steel

The microstructures and properties of coating from cemented carbide on the substrate of H13 by vacuum powder sintering were studied.The effect of sintering temperature on the microstructures of coating was discussed.The interface characteristics between coating and H13 steel substrate,microhardness distribution and wear resistance in the coating were analyzed.The coating from cemented carbide with thickness of 1-3 mm by vacuum powder sintering at temperature ranging from 1280℃to 1300℃was obtained.The experimental results indicated that the coating with microhardness of HV1600 favorable to wear resistance is strongly bonded with the H13 steel substrate by mutual diffusion and penetration of Fe,Cr,Mo,V in substrate towards the coating and W,Co,Ni in coating towards the substrate.     

Mierostrueture and Properties of Coating from Cemented Carbide on Surface of H13 Steel

The microstructures and properties of coating from cemented carbide on the substrate of H 13 by vacuum powder sintering were studied. The effect of sintering temperature on the microstructures of coating was discussed. The interface characteristics between coating and H 13 steel substrate, microhardness distribution and wear resistance in the coating were analyzed. The coating from cemented carbide with thickness of 1-3 mm by vacuum powder sintering at temperature ranging from 1280℃to 1300 ℃ was obtained. The experimental results indicated that the coating with microhardness of HV 1600 favorable to wear resistance is strongly bonded with the H 13 steel substrate by mutual diffusion and penetration of Fe,Cr, Mo,V in substrate towards the coating and W, Co,Ni in coating towards the substrate.     

Effect of Polypropylene Fibers on the Longterm Tensile Strength of Conerete

The influence of low volume fraction of polypropylene（PP） fibers on the tensile properties of normal and high strength concretes was studied. The experimental results indicate that the addition of PP fibers in concrete leads to a reduction in tensile strength during the age of 28 d. Whereas, after 28 days, there is a notable effect in tensile strength due to PP fibers restraining the formation and growth of microcracks in concrete, which improves the continuity and integrality of concrete structure, Thus, a low volume fraction of PP fibers is beneficial to enhancing the long-term tensile strength of concrete materials and improving the durability of concrete structures.     

Abrasive wear behaviors of high velocity arc sprayed iron aluminum composite coatings

The High Velocity Arc Spraying （HVAS） technology was used to prepare Fe-Al composite coatings by the adding of different elements into cored wires to obtain different Fe-Al coatings. The added compounds do great effect on the properties of the composite coatings. The microstructures and abrasive wear performances of the coatings were assessed by transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, and THT07-135 high temperature wear equipment. It was found that the adding of Cr3C2 can greatly increase the room temperature wear behavior, and Fe-Al/WC coatings have adapting periods at the beginning of wear experiment. With the rise of temperature, the wear resistance of Fe-AI/Cr3C2 coatings becomes bad from room temperature to 250℃, and then stable from 250℃ to 550℃; the wear resistance of Fe-Al/WC becomes well with the rise of temperature. The adding of Cr and Ni can also improve wear performances of Fe-Al composite coatings.     

Effects of Ta addition on the microstructure and mechanical properties of Ti_(40)Zr_(25)Ni_8Cu_9Be_(18) amorphous alloy

The effects of Ta addition on the microstructure and mechanical properties of Ti40Zr25Ni8Cu9Be18 bulk amorphous alloy were investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scan electron microscopy (SEM) and compressive testing. As a result, the addition of Ta (0-8at%) prompted the successive precipitation of quasicrystalline phase, CuTi2 phase and bcc β-Ti solid solution. Additionally, the addition of less Ta content (3at%-5at%) led to the formation of amorphous ma- trix/nanoquasicrystal/CuTi2 complex phase structure; and nanoquasicrystals, as reinforcement precipitates, improved the fracture strength of Ti-Zr-Ni-Cu-Be-Ta alloys, which led to the high compressive fracture strength 1856 MPa of Ta5 alloy. With increasing Ta content (5at%-8at%), although the ductile dendritic β-Ti solid solution was precipitated, the strength and plasticity decreased to a great extent resulting from the growth of quasicrystalline phase and CuTi2 phase.     

Abnormal gradient microstructure in Cr_3C_2 based cemented carbide

Ｃｒ3 Ｃ2 ｂａｓｅｄｃｅｍｅｎｔｅｄｃａｒｂｉｄｅｓａｒｅｃａｌｌｅｄｔｈｅ“ｓｔａｉｎｌｅｓｓｓｔｅｅｌ”ａｍｏｎｇｃｅｍｅｎｔｅｄｃａｒｂｉｄｅｓｆｏｒｔｈｅｉｒｕｎｉｑｕｅｐｒｏｐｅｒｔｉｅｓ ,ｓｕｃｈａｓｅｘｃｅｌｌｅｎｔｃｏｒｒｏ ｓｉｏｎｒｅｓｉｓｔａｎｃｅｉｎｖａｒｉｏｕｓａｃｉｄｓ,ｏｘｉｄａｔｉｏｎｒｅｓｉｓ ｔａｎｃｅａｔｈｉｇｈｔｅｍｐｅｒａｔｕｒｅａｎｄｃｏｍｐａｒａｂｌｅ ｔｏ ｓｔｅｅｌｔｈｅｒｍａｌｅｘｐａｎｓｉｏｎｃｏｅｆｆｉｃｉｅｎｔ,ｓｕｇｇｅｓｔｉｎｇａｇｏｏｄｗ…     

Abnormal gradient microstructure in Cr3C2 based cemented carbide

With OLYMPUS PMG3 metallograph, an abnormal three-layer gradient structure, i. e. coarse grain zone, binder enrichment zone and normal structure zone from surface to inner, was observed in Cr₃C₂ based cemented carbide. In the binder enrichment zone, three different shapes of anomalous coarse carbides were observed. It is shown that the transverse rupture strength can be raised remarkably, up 20.7% from the alloy with abnormal gradient structure by removing the abnormal gradient structure. The results suggested that the abnormal gradient structure in the surface, especially the anomalous coarse carbides in the binder enrichment zone is the main reason for the lower strength Biography of the first author: ZHANG Li, born in 1965, senior engineer, majoring in powder metallurgy.     

Effect of nitrogen introduction methods on the microstructure and properties of gradient cemented carbides

Gradient cemented carbides with the surface depleted in cubic phases were prepared following normal powder metallurgical pro-cedures.Gradient zone formation and the influence of nitrogen introduction methods on the microstructure and performance of the alloys were investigated.The results show that the simple one-step vacuum sintering technique is doable for producing gradient cemented carbides.Gradient structure formation is attributed to the gradient in nitrogen activity during sintering,but is independen...     

亚微细硬质合金三牙轮钻齿的使用与失效分析

将钴含量为13％的亚微细晶粒硬质合金钻齿应用到81／2XA537三牙轮钻头上，并运用扫描电镜和光学显微镜等手段对亚微细晶粒硬质合金钻齿进行了失效分析。分析发现81／2XA537钻头的主要失效形式为崩齿和断齿。在断口分析的基础上，提出了亚微细硬质合金断裂机理为沿晶断裂，而常规硬质合金的断裂机理为穿晶断裂。由于生产工艺问题亚微细合金内部存在粗大的WC晶粒、晶粒偏析以及微裂纹，这些内部缺陷的存在使亚微细合金出现早期失效。     

Rare earth doped new cemented carbide with Ni-Co binder for mining

ＴｈｅｗｅａｒｒｅｓｉｓｔａｎｃｅｏｆｔｈｅｔｒａｄｉｔｉｏｎａｌＷＣ Ｃｏｃｅ ｍｅｎｔｅｄｃａｒｂｉｄｅｆｏｒｍｉｎｉｎｇ ,ｗｉｔｈｔｈｅａｄｄｉｔｉｏｎｏｆｒａｒｅｅａｒｔｈ ,ｃａｎｂｅｉｍｐｒｏｖｅｄｏｂｖｉｏｕｓｌｙ[1] .Ｂａｓｅｄｏｎｔｈｅｉｎ ｈｅｒｅｎｔｓｉｍｉｌａｒｉｔｙｂｅｔｗｅｅｎＷＣ ＣｏａｎｄＷＣ Ｃｏ Ｎｉｃｅｍｅｎ ｔｅｄｃａｒｂｉｄｅｓｉｎｔｅｒｍｓｏｆｍｉｃｒｏｓｔｒｕｃｔｕｒｅ ,ｗｅｃａｒｒｉｅｄｏｕｔｔｈｅｓｔｕｄｙｏｆＷＣ Ｃｏ Ｎｉｃｅｍｅｎｔｅｄｃａｒｂｉｄｅｗ…     

Manufacture of the Ultrafine Grain WC/Co Cemented Carbides by Combined Sintering Processing

A new kind of sintering process, combined sintering process. i.e. vacuum sintering plus hot isolate pressure sintering (HIP), was introduced for producing ultrafine WC-10% Co (mass fraction. so as the follows) cemented carbides. The effects of some processing parameters on the microstructure and mechanical properties of the obtained cemented carbides were studied. The results show that the rapid shrinkage and the pronounced densification of tile cemented carbides took place during the vacuum sintering stage, which is intinaately correlated with the local liquid sintering occurred during this earl} sintering stage for the high surface activity of ultrafine WC-Co powder. The way of high pressure imposing. isothermal treatment cycle during ac.acuum sintering and HIP sintering stage directly influence the densitication of compacts and the mechanical properties of the produced WC-10%Co cemented carbides.     

Growth kinetics of cubic carbide free layers in graded cemented carbides

In order to reveal the formation mechanism of cubic carbide free layers (CCFL),graded cemented carbides with CCFL in the surface zone were fabricated by a one-step sintering procedure in vacuum,and the analysis on microstructure and element distribution were performed by scanuing electron microscopy (SEM) and electron probe micro-analyzer (EPMA),respectively.A new physical model and kinetic equation were established based on experimental results.Being different from previous models,this model suggests that nitrogen diffusion outward is only considered as an induction factor,and the diffusion of titanium through liquid phase plays a dominative role.The driving force of diffusion is expressed as the differential value between nitrogen partial pressure and nitrogen equilibrium pressure essentially.Simulation results by the kinetic equation are in good agreement with experimental values,and the effect of process parameters on the growth kinetics of CCFL can also be explained reasonably by the current model.     

Influences of Carbon Content on the Properties and Microstructure of Ultrafine WC-10Co Cemented Carbide

WC-10Co nanocrystalline composite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing (HIP). Influences of carbon content on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that the relative density of the ultrafine WC-10Co cemented carbides can reach 99.72%, and the transverse rupture strength (TRS) was higher than 3 890 MPa, Rockwell A hardness (HRA) was higher than 92.5, the average grain size was less than 460 nm, when carbon content in nanocrystalline composite powder was 5.54wt% and the ball-milled time was 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and homogeneous microstructure was obtained. Funded by the National Natural Science Foundation of China (No.50502026), the Youth Science Plan for Light of the Morning Sun of Wuhan City(No.200750731270), and Key Project for the Science & Technology Research Department, Chinese Ministry of Education (No.105123)     

球墨铸铁轧辊的光纤激光合金化性能

为了提高球墨铸铁轧辊的使用性能,采用光纤激光合金化系统对轧辊表面的预置合金层进行激光扫描,在球墨铸铁轧辊表面形成了冶金结合的合金化层.在最佳工艺参数条件下,分析了合金化层的耐磨性能、维氏硬度、冷热疲劳性能和显微组织.结果表明,合金化后的球墨铸铁轧辊的耐磨性能约为基体的3倍,维氏硬度也得到了明显提高,冷热疲劳性能基本相同.合金化层由亚共晶组织构成,亚共晶组织初晶相由马氏体(M)、未分解WC硬质相及共晶组织构成,共晶组织由马氏体(M)与复杂碳化物(WC、Co6W6C和Fe3C)构成.合金化层深度约为0.4 mm且组织细小.