Mechanical properties of WC–Co coatings with different decarburization levels

In this study, two kinds of WC–Co coatings with different decarburization levels were deposited by high-velocity oxy-fuel(HVOF) spraying using the ultrafine WC–Co composite powder and commercial micronsized powder, respectively. The hardness and elastic modulus were measured on the top surface and cross sections of the prepared coatings by the nanoindentation method. The results show that the ultrafine-structured coating has much higher density and inhibited decarburization than the conventional coating, which thus results in higher hardness and elastic modulus values than the micronsized coating. The wear resistance of thermal-sprayed cermet coatings greatly depends on the cross-sectional hardness and elastic modulus which reflects the bond strength between splats to some extent. Based on the analysis, a better understanding of the microstructure and properties in cermet coating materials was obtained.     

Internal Mechanism Analysis of Modeling on Particles Size Distribution Characteristics of Impact Attrition Beryllium Powders

基于铍(Be)冲击制粉颗粒的形貌特征,建立了一个描述Be粉颗粒尺寸分布的物理模型,该模型仅含一个物理意义明确的参数。模型中考虑了2种重要的内在影响机制:具有不同初始动能的颗粒在完成冲击后的存在状态应该遵从Maxwell-Boltzmann分布,即大颗粒具有高的能量,状态不稳定,在冲击过程中容易碎成小颗粒,这一影响可以用颗粒尺寸的负指数函数来描述;获得低表面能的倾向又使得颗粒尽可能具有大的体积,这一影响可以用颗粒尺寸的立方函数来描述。实际的颗粒尺寸分布是这2种影响竞争的结果。计算结果与实验数据符合得很好。     

沉积时间对钼薄膜结构和热疲劳性能的影响

采用直流磁控溅射在不同沉积时间条件下制备钼薄膜,并用电子束热负荷装置对薄膜进行热疲劳性能试验,利用X射线衍射仪(XRD)对其结构和残余应力状态进行测试分析,用扫描电镜(SEM)对钼薄膜热疲劳前后形貌进行表征。结果表明:薄膜沿(110)取向择优生长,呈柱状晶结构,薄膜内存在张应力,残余应力随沉积时间增加而逐渐减小。热循环试验后均未出现薄膜脱落现象,但均产生表面裂纹。随着沉积时间由4h增加至8h,疲劳裂纹由穿晶断裂的直线裂纹转变为沿晶开裂的曲折裂纹,同时成膜过程中的退火效应使薄膜的晶粒长大、晶粒结构更加趋于完整、残余应力减小,从而使薄膜疲劳裂纹减小。     

氧化-还原碳化法回收再生高性能硬质合金的研究

以废旧WC-Co硬质合金为原料,采用氧化和原位还原碳化的短流程方法合成再生WC-Co复合粉末,随后对再生复合粉低压烧结得到再生硬质合金。利用XRD、SEM和TEM等对再生复合粉和再生硬质合金的物相和显微组织形貌进行观察和分析,系统研究了原料粉末中配碳量对再生复合粉和再生合金的物相组成和力学性能的影响。配碳量为16.60%时制备的再生WC-16%Co(质量分数,下同)硬质合金的断裂韧性为24.80 MPa·m1/2、横向断裂强度达到3860MPa,并且分析了再生硬质合金的显微组织与性能之间的关系。     

粉末致密度对碳化钨涂层结构特征的影响

利用超音速火焰喷涂技术将4种不同致密度WC10Co4Cr粉末制备成涂层。采用扫描电镜、X射线衍射仪、显微硬度计、表面粗糙度仪等设备对涂层的微观组织、结构特征进行分析。结果表明,随着致密度的降低,团聚烧结型粉末与基体撞击后更容易铺展,碳化钨微粒分布变得更均匀,形成的涂层具有更低的孔隙率和表面粗糙度;但是随着致密度的降低,碳化钨分解率升高,形成更多的脆硬相,最终使得涂层断裂韧性下降。由此可知,致密程度影响粉末颗粒在热喷涂过程中加热、加速和铺展状态,从而影响涂层的结构特征。     

复合添加晶粒长大抑制剂对WC-Co复合粉烧结硬质合金的影响

在超细WC-Co复合粉中复合添加不同含量的晶粒长大抑制剂VC和Cr3C2,利用X射线衍射仪分析粉末及硬质合金的物相组成,通过扫描电镜和透射电镜观察硬质合金的形貌,研究不同含量的晶粒长大抑制剂对硬质合金的显微组织和力学性能影响规律。结果表明:随着晶粒长大抑制剂的增加,晶粒异常长大现象消失,晶粒细小均匀;同时发现在WC-Co复合粉中VC的增加可以快速提高硬质合金的硬度,而适量的Cr3C2可以有效提高硬质合金的横向断裂强度。     

预镀铜对磷青铜/钢双金属材料界面性能的影响

在钢板表面预电镀铜成功制备了界面结合强度较高的磷青铜/钢双金属材料.采用扫描电子显微镜(SEM)及其配备的能谱仪(EDS)分析了界面的微观组织和化学成分;采用压剪试验测试了双金属材料的界面结合强度.结果表明,钢板表面预镀铜能阻止磷元素扩散到钢板而形成富磷脆性相,避免界面处出现裂纹,显著提高了磷青铜涂层界面的结合强度.     

Laser cladding of continuous caster lateral rolls: Microstructure,wear and corrosion characterisation and on-field performance evaluation

Laser cladding has been used to improve the service life of lateral rolls which experience high temperature wear and corrosion in the zero segment zone of continuous slab caster. Three different compositions of nickel base powders with varying chromium, molybdenum, boron and niobium content with different wear and corrosion resistance properties have been used as cladding consumables. The microstructure of the clad layers shows a two phase cellular dendritic structure, with nickel–chrome dendrites surrounded by hard phases rich in chromium and boron or niobium. Hard precipitates contribute to wear resistance whereas the presence of chromium along with molybdenum in nickel-rich matrix improves resistance to corrosion. Actual performance results suggest that the powder material with higher wear resistance property gives the maximum life when the corrosion conditions are less hostile. In rolls cladded with highest boron and nickel containing powders, the layers were intact, whereas fine cracks and de-lamination was observed in the other rolls.     

添加WC的铁基Fe55粉末重熔层的组织与性能

研究了氩弧重熔条件下,铁基Fe55粉末中加入WC所形成重熔层的组织与性能。结果表明,重熔层组织由带状平面晶、胞状树枝晶和细小等轴晶组成,物相主要为马氏体、Cr_9.1Si_0.9、Cr₇C₃和Fe₇W₆。重熔层硬度及耐磨性较基体有显著提高,且重熔层表层硬度较次表层略低。