Search

Highlights: [•] Glycine doped MgB2 can be made at low temperature by Cu-activated sintering. [•] We obtained excellent J c in glycine-doped MgB2 sintered at 600°C for 15h. [•] Cu and glycine have synergistic effects on improvement of J c. [•] We illustrated the precipitation morphologies of secondary phase MgCu2 and MgO phases. [ABSTRACT FROM AUTHOR]

Abstract: The present study examines the effect of solidification rate on the type and morphology of intermetallic compounds (IMCs) of Al-based alloy with high Fe and Si contents in a wide cooling rate range of 1–100K/s. It was found that the final microstructure of Al–14wt.% Fe–2wt.% Si alloy mostly depends upon the solidification rate, which suggests that different solidification rates produced dissimilar microstructures. The increase of cooling rate significantly affects the phase selection sequence, amount and morphology of the IMCs in Al–14wt.% Fe–2wt.% Si. [Copyright &y& Elsevier]

Abstract: The effect of small additions of In, up to 1wt.%, on the microstructure of the eutectic Sn–3.7wt.%Ag–0.9wt.%Zn solder was investigated. As observed by microstructural analysis, the increase of In content made β-Sn easy to form but suppressed the formation of the AgZn phase in the Sn–3.7Ag–0.9Zn solder. After annealing at 473K for 20 and 50h, the microstructure varied a lot in the morphology of the investigated Sn–Ag–Zn–In solder. The β-Sn dendrites grew coarser but dimmer accompanied with the segregation of the intermetallic compounds (IMCs) along their boundaries. Furthermore, the suppressed Ag–Zn IMCs formed in the Sn–3.7Ag–0.9Zn–1In solder. And the coarsening of the β-Sn dendrites and the growth of IMCs particles in the microstructure of the samples brought a significant softening during annealing of the investigated Sn–Ag–Zn–In alloys. [Copyright &y& Elsevier]

Abstract: The structural stability of the rapidly solidified eutectic Sn-3.7wt.%Ag-0.9wt.%Zn solder was explored by aging at room temperature (298K). After aging for 2 weeks, the microstructure varied a lot in the morphology of intermetallic compounds (IMCs) in the investigated Sn–Ag–Zn solder. Dot-like Ag3Sn IMCs in the rapidly solidified solder congregated and formed bulk ones in order to minimize the system energy, which is contrary to a stable microstructure in the slowly cooled specimen. It seems that the coarsening of the IMCs in the microstructure of the rapidly solidified specimen brought a significant softening during aging of the explored Sn–Ag–Zn alloy. Furthermore, with the addition of zinc, the solder system becomes harder than the eutectic Sn–Ag system and the Ag–Zn phase dispersed in the eutectic Sn–Ag–Zn solder could strengthen the system as a reinforcing secondary phase. [Copyright &y& Elsevier]

Abstract: The effect of addition of In, up to 1wt.%, on the formation of intermetallic compounds (IMCs) in the solidified Sn–3.7%Ag–0.9%Zn lead-free solder was investigated. As observed by microstructural analysis, the typical structure of Sn–Ag–Zn solder is composed of β-Sn phase and mixed granules of Ag3Sn and AgZn IMCs. After alloying with In, it evolves into a mixture of randomly distributed rods and granules of Ag3Sn and AgZn. Clearly, the addition of In into the explored Sn–Ag–Zn solder promotes the formation of rod-like IMCs for the reason that the growth competition of the Ag3Sn and AgZn IMCs was destroyed by the selective adsorption of In atoms on a certain preferable crystalline planes of the separated IMCs. The change in the morphology of the formed IMCs leads to a great difference in the mechanical performances, for example, the measured microhardness of the investigated solders evolves from 16.95HV to 21.35HV with the increase of In content. [Copyright &y& Elsevier]

In order to better understand the thermal stability and mechanical properties of the nominal Ti–22Al–25Nb alloy with different initial microstructures, microstructural evolution after long-term aging, and mechanical properties at room temperature and 650 °C of four differently heat-treated Ti–22Al–25Nb alloy were investigated. The investigation results indicated that α 2 platelets formed by aging at (α 2 +B2) region were not as stable as previous research claimed and spontaneously decomposed into fine (O+β/B2) mixture during the annealing at 650 °C. As a result, the alloy's steady-state creep strain rate dropped dramatically at the secondary creep stage and tensile strength grew. On the contrary, long time aging exposure resulted in the connection of original dispersed lenticular O precipitation and thus degraded the ductility of all specimens. Besides, the discontinuous precipitation B2→β+O caused by supersaturation of solutes in the matrix also harmed the mechanical properties. Under the condition of 650 °C/250 MPa, the steady-state creep strain rates of the Ti–22Al–25Nb specimens show a significant dependence on their grain size. Crept samples showed that most dislocation motion was restrained in the β channels under a small strain and then extended into O phase when creep strain grew over 10%. Finally, by comparing the room temperature tensile property and creep resistance of four samples, supertransus solution and furnace cooling ensured the alloy most balanced mechanical properties among lamellar samples. The supertransus then furnace-cooled sample did not only have an excellent creep resistance but also kept a moderate room temperature elongation to failure of nearly 6%. • Thermal stability and mechanical properties of four different microstructures were investigated and compared. • Metastability of α 2 phase resulted in its decomposition and promoted the creep resistance of the alloy. • Grain size including equiaxed precipitation dominates creep resistance in intermediate stress regime. • Discontinuous precipitation and piling up of dislocations promoted the interfacial cracks. [ABSTRACT FROM AUTHOR]

In this paper, the effects of hafnium (Hf) addition on the thermal stability of the microstructure and tensile properties of Al-containing 16Cr-ODS steels were investigated. High temperature aging tests of the ODS steels with and without Hf were conducted at 750 °C, 950 °C and 1150 °C for 100 h respectively. And the microstructure evolution after thermal aging was investigated using transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results indicated that Hf addition could improve the coarsening resistance of the oxide particles and the grains during aging treatment due to the formation of stable Y 2 Hf 2 O 7 particles. Tensile tests on the aged-steels showed that the ultimate tensile strength and yield strength of 16Cr-Hf-ODS steel were higher than those of 16Cr-ODS steel. It was considered that the excellent thermal stability and tensile properties of 16Cr-Hf-ODS steel were related with the refined microstructure. [ABSTRACT FROM AUTHOR]

After solution treatment at 520 °C for 6 h and subsequent aging at 200 °C for 6 h, eutectic Mg 2 Si phase in Al–10%Mg 2 Si alloy transforms from long rod to short fiber-like and spherical morphologies, and a great number of nano-sized β″ particles precipitate in the Al matrix. The fine eutectic Mg 2 Si phase combined with nano-sized precipitates gives rise to enhanced hardness and high tensile strength of Al–10%Mg 2 Si alloy (increasing from 186 MPa to 234.6 MPa). [ABSTRACT FROM AUTHOR]

The present work investigates the change in the microstructure and the improvement in the microhardness in the Mo-modified Ti 2 AlNb alloys induced by solution treatment. Typical Widmanstätten O + B2 structure was observed in the alloys directly aged in the O + B2 phase region, with a lower hardness value compared to that of the alloy without Mo addition. Well-arranged O + B2 colonies were observed in the specimen solution treated in single B2 phase region, and it exhibited a favorable hardness performance of up to 620 HV. Besides the precipitation hardening of the O phase, the solution of Mo in B2 phase should be responsible for the enhancement of hardness. Further microstructural observation proved that the substitution of Mo for Nb in the lattice of B2 phase induced the lattice distortion mainly the (200) and (211) planes, and the induced entanglement of dislocations also contributed to the enhancement of hardness. Image 1 • Well-arranged O + B2 structure is obtained in Ti 2 AlNb alloys by Mo addition. • Solution treatment and ageing enhanced hardness of Mo-modified Ti2AlNb alloys. • Lattice distortion of B2, especially along (211) face, is induced by adding Mo. • Orientation relationship of (211) B2 //(26 1 ¯ ) O is identified in the aged Ti 2 AlNb alloy. [ABSTRACT FROM AUTHOR]

The effect of primary O phase on thermal compressive deformation behavior of a Ti 2 AlNb-based alloy are investigated at temperatures from 990 °C to 1020 °C and strain rate range from 0.001 s−1 to 1 s−1. The results indicated that the primary O phase has a significant effect on the hot deformation behavior of the studied alloy. The peak stress and the degree of the stress descent of the specimen with primary O lath and Widmanstätten O + B2 structures are higher than those of the specimen with Widmanstätten O + B2 structures under higher strain rate. Besides, both the critical stress and critical strain for the onset of dynamic recrystallization (DRX) of the studied alloy upsurge with increasing the strain rate or decreasing the deformation temperature. The specimen with primary O lath and Widmanstätten O + B2 structures exhibits greater critical stress and critical strain than the specimen with Widmanstätten O + B2 structures. The strain rate sensitivity exponents of the investigated alloy with primary O lath and Widmanstätten O + B2 structures is higher than that of the alloy with Widmanstätten O + B2 structures at low temperature (990 °C), while the reverse is true at high temperature (1020 °C). Beyond that, the DRX mechanisms of the explored alloys with different morphologies of O phase were also investigated by EBSD and TEM analysis. • Thermal deformation behavior of Ti 2 AlNb-based alloy with two morphologies of O phase was studied. • The existence of primary O lath results in more significant effect of flow softening. • Critical conditions for the onset of DRX is sensitive to morphology of O phase. • The studied Ti 2 AlNb-based alloys with different morphologies of O phase undergo DDRX in all deformation conditions. [ABSTRACT FROM AUTHOR]