表面粗糙度对Ni-20Cr合金高温氧化行为的影响

表面粗糙度作为重要的参数,对合金高温氧化膜剥落有重要影响.为此,研究表面粗糙度对Ni-20Cr合金氧化20 h内的氧化动力学及氧化膜剥落行为的影响.通过热重法绘制动力学曲线,可以看出2.5 μm砂纸磨痕的合金氧化速率明显低于90 μm砂纸磨痕的氧化速率.利用扫描电镜观察氧化膜表面形貌,显示粒状的氧化物在2.5 μm砂纸磨痕合金表面生成,而刻面状的氧化物在90 μm砂纸磨痕合金表面形成.XRD分析表面,在2.5 μm砂纸磨痕合金表面生成的氧化物为Cr2O3,在90 μm砂纸磨痕表面形成的氧化物为NiO.结果表明：平滑的Ni-20Cr合金表面有利于生成保护性的Cr2O3而不发生脱落,具有优良的抗氧化性能.     

7050铝合金热挤压成形过程的有限元模拟

针对传统工程机械用销轴数量多、重量大、工况差等不足,以7050高强轻质铝合金代替传统钢质材料,采用DEFORM‐3D有限元分析软件,对7050铝合金热挤压成形过程进行有限元数值模拟,分析了挤压载荷、金属流动速率、等效应变、等效应力和温度场等参量的变化规律。结果表明,销轴的热挤压变形过程可分为4个阶段,即挤压填充阶段、开始挤出阶段、稳定挤压阶段和终了挤压阶段;工件内部等效应变分布横向均匀性较好,除了尾部变形不均匀外,其他部位应变分布基本一致;在挤压凹模模口处形成死区,工件内部等效应力达到最大值。     

Guide for Authors

<正>The journal of"Progress in Natural Science:Materials International(PROG NAT SCI-MATER)"sponsored and organized by both Chinese Materials Research Society(C-MRS)and Inter national Union of Materials Research Societies(IUMRS)started to publish     

一种黑曲霉斜面培养基的优化方法

通过一系列实验,优化了黑曲霉Co827的斜面培养基配比.优化后的斜面培养基为3.5°Be～ 3.6°Be麦芽汁培养基.采用优化后的培养基,单菌落孢子数达到167.2×105左右,产孢子能力提高了15.07％,通过摇瓶验证,产酸达到14.40％,提高了3％左右.     

Effects of Cr and Mo elements on the microstructures and compressive properties of the in situ (TiC_xN_y–TiB_2)/Ni cermets

In-situ(TiC_xN_y–TiB_2)/Ni cermets with 70 wt%TiC_xN_y–TiB_2 were successfully fabricated by combustion synthesis and hot pressing sintering in Ni-Ti-B_4C-BN powder systems.The microstructures,density,compressive properties,and hardness of the TiC_xN_y–TiB_2/Ni cermets with the addition of 0–8 wt%Cr/Mo to the Ni-Ti-B_4C-BN powder systems were compared and analysed.The results showed that the ceramic particles distributed uniformly in the cermets,and the size of the ceramic particles reduced with the Cr/Mo addition.Both Cr and Mo addition can improve the hardness,compressive properties,and fracture strains of the cermets.The hardness,compressive strength,and fracture strain of the(TiC_xN_y–TiB_2)/(Ni+Cr)cermets increased from 1561 HV,2.94 GPa,and 2.9%to 1864 HV,3.65 GPa,and 3.4%,respectively when the Cr content increased to 5 wt%.The hardness and compressive strength of the(TiC_xN_y–TiB_2)/(Ni+Mo)cermets increased from 1561 HV and 2.94 GPa to 1902 HV and 3.43 GPa,respectively when the Mo content increased to 8 wt%.The cermets with Cr had better compressive properties than the cermets with Mo.     

Studies on induction hardening of powder-metallurgy-processed Fe-Cr/Mo alloys

Induction hardening of dense Fe-Cr/Mo alloys processed via the powder-metallurgy route was studied. The Fe-3Cr-0.5Mo, Fe-1.5Cr-0.2Mo, and Fe-0.85Mo pre-alloyed powders were mixed with 0.4wt%, 0.6wt%, and 0.8wt% C and compacted at 500, 600, and 700 MPa, respectively. The compacts were sintered at 1473 K for 1 h and then cooled at 6 K/min. Ferrite with pearlite was mostly observed in the sintered alloys with 0.4wt% C, whereas a carbide network was also present in the alloys with 0.8wt% C. Graphite at prior particle boundaries led to deterioration of the mechanical properties of alloys with 0.8wt% C, whereas no significant induction hardening was achieved in alloys with 0.4wt% C. Among the investigated samples, alloys with 0.6wt% C exhibited the highest strength and ductility and were found to be suitable for induction hardening. The hardening was carried out at a frequency of 2.0 kHz for 2-3 s. A case depth of 2.5 mm was achieved while maintaining the bulk (interior) hardness of approximately HV 230. A martensitic structure was observed on the outer periphery of the samples. The hardness varied from HV 600 to HV 375 from the sample surface to the interior of the case hardened region. The best combination of properties and hardening depth was achieved in case of the Fe-1.5Cr-0.2Mo alloy with 0.6wt% C.     

Development of liquid-nitrogen-cooling friction stir spot welding for AZ31 magnesium alloy joints

A liquid-nitrogen-cooling friction stir spot welding (C-FSSW) technology was developed for welding AZ31 magnesium alloy sheets. The liquid-nitrogen cooling degraded the deformability of the welded materials such that the width of interfacial cracks increased with increasing cooling time. The grain size of the stirred zone (SZ) and the heat-affected zone (HAZ) of the C-FSSW-welded joints decreased, whereas that of the thermomechanically affected zone (TMAZ) increased with increasing cooling time. The maximum tensile shear load of the C-FSSW-welded joints welded with a cooling time of 5 or 7 s was larger than that of the friction stir spot welding (FSSW)-welded joint, and the tensile shear load decreased with increasing cooling time. The microhardness of the C-FSSW-welded joints was greater than that of the FSSW-welded joint. Moreover, the microhardness of the SZ and the HAZ of the C-FSSW-welded joints increased, whereas that of the TMAZ decreased, with increasing cooling time.     

ZrO2添加量对等离子放电烧结制备WC-6Co组织和性能的影响

以WC-6Co为主体原料，通过添加不同含量的ZrO₂作为烧结助剂，采用SPS烧结技术制备出性能出众的WC-6Co硬质合金，研究了ZrO₂烧结助剂对硬质合金显微组织及力学性能的影响规律.结果表明:随着ZrO₂添加量的增加，试样的显微组织更加致密，相对密度更大，硬度和断裂韧性也有一定程度的增加.并且，当添加ZrO₂的质量分数为3%时，试样的相对密度达到96.7%，维氏硬度增加到20.28kN·mm^-2，断裂韧性增长到12.7MPa·mm^1/2，综合性能最优.研究发现，ZrO₂可以通过促进离子的扩散和颗粒的重排促进烧结，最终使得材料的相对密度和性能均得到提升.     

基于多材质复合管柱的裸眼井壁支撑工艺及应用

已完钻超深裸眼水平井侧钻技术是经济、高效开发油藏剩余油的主要手段之一，传统的磨铣钢套管开窗侧钻技术存在下入摩阻大、磨铣耗时长导致开窗失败等问题。为此，提出了基于多材质复合管柱的超深水平井裸眼井壁支撑工艺，结合中国西北油田已完钻超深裸眼水平井井况，首先，提出了基于“铝合金+碳钢”的多材质复合管柱组合及设计方法；其次，开展了基于管柱实物屈曲实验数据的管柱临界屈曲载荷计算模型适用性评价，并优选出了适合于“铝合金+碳钢”多材质复合管柱的屈曲临界载荷计算模型；最后，研究了综合考虑管柱扭矩、摩阻、刚性、井眼条件、管柱强度及材质的多材质复合管柱下入性分析方法，并利用下入性分析软件对西北油田顺北X1井、X2井、X3井、X4井复合管柱进行了下入可行性评价。该方法在X1井和X2井得到成功应用，进一步论证了该工艺现场应用的可行性。研究成果可为超深水平井裸眼井壁支撑的复合管柱设计和下入可行性评价提供理论参考。     

振动对ZL205A合金偏析组织及硬度的影响

为了解决ZL205A合金铸件产生偏析缺陷等问题，进一步明确振动对偏析组织及硬度的影响规律，采用电磁式振动台作为振动源，探究了振动频率、振幅、振动时间对合金偏析组织占比及硬度的影响情况。结果表明，振动频率在25~55 Hz内变化时，随着振动频率的增加，偏析组织占比呈现先减小、后增加的趋势，硬度呈现先增大、后减小的趋势；振幅由1 mm增加到4 mm的过程中，偏析组织占比逐渐减少并趋于稳定，硬度呈现先减小、后增大的趋势；振动时间由30 s增加至75 s时，偏析组织占比呈现增加趋势并最终趋于稳定，硬度呈现先减小、后增大的趋势。振动频率对合金偏析组织和硬度的影响最为显著，振动时间和振幅的影响次之，此外，偏析组织的析出也会影响合金硬度。研究结果为明确ZL205A合金在振动条件下凝固组织的变化规律、提高铸件质量提供了理论参考。