炭黑含量对反应烧结碳化硅组织与性能的影响

研究了炭黑含量对反应烧结碳化硅浆料工艺参数以及烧结体力学性能的影响,分析了坯体中碳含量过高,烧结时产生炸裂和内部"夹生"的原因,并对不同碳含量的坯体烧结后的试样进行了微观组织和相组成分析。

Creep Behaviors of DA Casting and Rolling GH4169 Superalloy

After the billet of Casting and Rolling GH4169 alloy was directly aged (DA) treated at 720 ℃ and 620 ℃, creep behavior and deformed features of the alloy were investigated by means of the measurement of creep curves and microstructure observation. Results show that the DA Casting and Rolling GH4169 Superalloy displays a lower strain rate during creep and longer lifetimes under the condition of the applied stress of 700 MPa at 650 ℃ , the creep lifetimes of the alloy decrease to 127 h as temperature is elevated to 660 ℃ , and therefore the alloy exhibits an obvious sensitivity of the applied temperatures. During creep, the deformation mechanism of the alloy is thought to be the twinning deformation and slipping of dislocation within the twinning regions. Thereinto, the dislocation slipping of the single and double orientations occur within the twins. As creep enters the tertiary steady state stage, the micro-crack appears on the grains boundaries along the direction vertical to the applied stress axis, and expands along the grain boundary up to fracture.

一种镍基单晶合金高温蠕变期间的变形特征及元素分布

通过对一种6%Re/5%Ru镍基单晶合金进行高温蠕变性能测试、组织形貌观察及三维原子探针成分分析,研究了合金高温蠕变前后的元素分布及蠕变过程中的变形特征。结果表明,完全热处理后Al和Ta元素主要分布在合金的γ′相中。合金在1120℃/165 MPa条件下蠕变断裂后,元素在γ/γ′两相的分布发生改变,其中,Al、Ta、Cr和Co因为氧化作用导致在γ/γ′两相中的浓度均降低。此外,一部分Re、Ru、W和Mo原子富集于γ/γ′相过渡区域附近的γ基体一侧,可引起晶格畸变,增加位错运动的阻力,延缓位错剪切进入γ′相,是含Re/Ru合金具有较好高温蠕变抗力的原因之一。蠕变后期,切入相的位错可由{111}面交滑移至{100}面形成K-W锁,其保留的高数量K-W位错锁可抑制位错滑移和交滑移,是合金有较好蠕变抗力的原因之一。

Influence of Pre-Compressive Creep on Internal Friction Stress and Creep Parameters of Nickel-Base Single Crystal Superalloys

By means of pre-compressive creep treatment, the cubic γ′ phase in a nickel base single crystal superalloy is transformed into the P-type rafted structure. And the influence of the pre-compressive creep on the internal friction stress and creep lifetimes of the superalloy are investigated by means of the measurement of the creep curves and microstructure observation. Results show that, compared to the P-type structure alloy, the full heat treated state alloy displays a bigger internal friction stress value of dislocation motion during steady state creep and a longer creep lifetimes. The creep activation energies of the full heat treated and P-type structures alloys are measured to be 462 kJ/mol and 412 kJ/mol, respectively. Thereinto, the P-type rafted γ′ phase in the alloy is transformed into the N-type structure during tensile creep. And the N-type γ′ phase transformed from the P-type structure displays a shorter size in length, this is a main reason of the P-type structure alloy possessing a shorter creep lifetimes due to creep dislocation moving easily over the rafted γ′ phase.

Hot Corrosion Behaviors of Ni-14%Cr Alloys in Molten Sulfate

The corrosion behaviors and mechanism of Ni-14%Cr alloys in molten salt with Na2SO4 at 1000℃ was investigated by means of XRD analysis and SEM observation. Results show that the alloys were subjected to the accelerated corrosion in molten salt and the corrosion kinetic of the alloy obeys the parabolic law. On the other hand, the corrosion-resistance of the alloy could be improved significantly by increasing of chromium content. Corrosion products may be divided into three layers, i. e. NiCr2O4, CoCr2O4, CoNi2S4, AlWO3 and Al2O3 granule are included in the outside of the scales, the continuous Al2O3 layer is localed in intermediate layer, and the sulfides is in the internal layer. The Cr2S3 phase in Ni-14Cr prevents the S and O from the matrix of the alloy. The morphology examinations tend to support the sulphidization-basic dissolution model previously proposed for hot corrosion mechanism.

SINTERING BEHAVIOR OF Cu-Al ALLOY POWDER

The dynamic behaviour of transient liquid phase during sintering 5wt% Al-Cu alloy compacts with green density of 7.56g/cn￣3 is observed by means of high temperature metallographic microscopy. The structures and precipitating order of the phases are identified by means of DTA, TEM and composion analysis at the definite point and phase diagram. The results show that little Al-rich liquid phase resulting from eutectic reaction flows into the capillaries in Cu powder, because the peritectic reactions exhausts the liquid in high density compact,the composition homogenization needs longer sintering time. The remainder γ2-phase is discovered at place of the neck of sintered Cu particle and has a crystallographic relationship of (111)_(Cu)∥(033)_γ_2 after alloy is sintered at 900 ℃for 3h.

镍基单晶合金高温蠕变变形与损伤行为

通过蠕变性能测试和组织观察,研究了镍基单晶合金在高温蠕变期间的变形和损伤行为。结果表明,该合金在1040℃/137MPa条件下的蠕变寿命为556 h,表现出优异的蠕变抗力。合金在稳态期间的蠕变特性是位错在γ基体中滑移和攀移越过筏状γ′相。在蠕变后期,合金的变形特征是位错剪切进入筏状γ′相,剪切γ′相的位错可以交滑移,形成的Kear-Wilsdorf(K-W)锁可抑制位错的滑移和交滑移。位错的交滑移能够促使筏状γ/γ′两相的扭曲,致使沿γ/γ′界面的裂纹萌生及界面断裂,这是合金的损伤和断裂特征。而σ>η/α被认为是裂纹发生失稳扩展的条件。

热处理对DZ125定向凝固合金组织结构与蠕变行为的影响

通过不同条件蠕变性能测试及组织形貌观察,研究了热处理对DZ125合金的组织结构演变和蠕变行为的影响规律。结果表明,铸态合金的枝晶间区域存在较多放射状的共晶组织,在枝晶间和枝晶干处部分γ′相呈蝶形形态且γ′相尺寸具有较大差异。铸态合金的共晶组织及γ′相在固溶过程中被溶解,并在随后的冷却过程中类菱形的细小γ′相自γ基体中析出;一次时效期间,类菱形的细小γ′相发生钝化并长大直至转变成立方体形态;二次时效期间,γ′相的尺寸基本不变,但立方度增加,合金的组织结构为γ′相以共格方式自γ基体中析出。在热处理过程中基本消除了合金中的共晶组织,并提高了γ′相的立方度,但并未消除合金中的组织不均匀性,枝晶干区域的立方γ′相尺寸细小,而枝晶间区域的立方γ′相尺寸粗大,并且合金在980℃具有良好的抗蠕变性能。

Creep Behaviors of FGH95 Powder Ni-Base Superalloy

This article makes an investigation into the creep behavior and deformation features of FGH95 powder Ni-base superalloy by means of creep curves and microstructural observation. Results show that this superalloy exposes obvious sensibility to the applied temperature and stresses in the experimental range. Microstructure of the alloy consists of γ＇ phase of various sizes and dispersed carbide particles precipitated in the wider crystal boundaries between the powder particles. During the creep, the deformation of the alloy occurs in the form of singleor double-oriented slipping inside the grains, and some of the finer carbide particles are precipitated near the slipping traces. The wide grain boundaries might be broken into the finer grains due to severe deformation. The deformation mechanism of the alloy during creep is thought to be the activation of dislocations of double-oriented slipping, including （1/2）〈 110〉 dislocation inside the γ matrix phase and 〈110〉 super-dislocation inside the γ＇phase. The formation of the stacking faults and （1/3）〈112〉 super-Shockleys partial dislocation configuration is attributed to the decomposition of 〈 110〉 super-dislocation in the γ＇ phase.

单晶镍基高温合金超高温蠕变期间的变形机制

通过蠕变性能测试及组织形貌观察,研究了6%Re-5%Ru(质量分数)单晶镍基高温合金的超高温蠕变行为和变形机制。结果表明,该合金在1160℃/120 MPa条件下的蠕变寿命为206 h。稳态蠕变期间,位错在基体中滑移和攀移越过筏状γ′相是合金的变形特征,基体中溶解的高浓度难熔元素可增加位错运动阻力。蠕变后期,切入筏状γ′相的位错可由{111}面交滑移至{100}面,形成Kear-Wilsdorf(K-W)位错锁,高数量K-W位错锁可抑制位错滑移和交滑移,是合金具有较好蠕变抗力和较低应变速率的原因。交滑移可扭曲筏状γ′相,并在两相界面发生裂纹萌生与扩展,直至断裂,这是合金蠕变后期的变形与损伤特征。其中,溶入γ′相的Ru原子可替换Al原子,合金中Ru与Re、W的相互作用使较多的Re、W原子溶入γ′相,延缓元素扩散速率,阻碍位错运动,使合金在超高温蠕变期间仍保留高数量K-W位错锁及良好蠕变抗力。