Microstructure Of Bulk Alloys Research Articles

Influence of Heat Treatment and Deformation on the Structure, Phase Transformation, and Mechanical Behavior of Bulk TiNi-Based Alloys

We present a brief overview of the structural and phase transformations and mechanical properties of bulk binary TiNi shape memory alloys, which demonstrate attractive commercial potential. The main goal of this work was to create a favorable microstructure of bulk alloys using both traditional and new alternative methods of thermal and thermomechanical processing. It was found that the implementation of an ultrafine-grained structure by different methods determined an unusual combination of strength, ductility, reversible deformation, reactive resistance of these alloys to subsequent tensile or torsion tests at room temperature, and, as a consequence, the highly reversible effects of the shape memory and superelasticity. It is shown that the alloys Ti49.8Ni50.2 and Ti49.4Ni50.6 are incapable of aging, and, after being subjected to ECAP, were characterized by their high strength (σu up to 1200 MPa) and ductility (δ up to 60–70%). A combined treatment of multi-pass rolling and HT of the Ti49.5Ni50.5 and Ti49Ni51 alloys prone to aging have provided even greater strength (σu up to 1400–1500 MPa) with slightly lower ductility (25–30%). The microstructure, phase composition, and martensitic transformations in Ti-Ni alloys with varying Ni concentrations ranging from 50 to 51 wt.% were investigated by TEM, SEM, and X-ray methods. The mechanical behavior of the alloys was studied during tensile and torsion tests.

Microstructure evolution and magnetic properties of the Nd9Fe81–xTi4C2Nb4Bx (x=11, 13, 15) bulk magnets prepared by copper mold suction casting

The bulk nanocomposite magnets of Nd9Fe81–xTi4C2Nb4Bx (x=11, 13, 15) in sheet form with the thickness of 0.7 mm were prepared by copper mold suction casting and subsequently annealing. The microstructure evolution and magnetic properties of bulk magnets were studied. It was shown that the as-cast microstructure of bulk alloys were composed of Nd2Fe14B, α-Fe, Fe3B crystalline phases and an amorphous matrix, and that the glass formability of alloy was improved with increasing the B content. The DSC analysis showed that the as-cast bulk alloys had the crystallization behavior of a two-step process. After annealing at the temperatures which was 40–63 K higher than their onset temperatures of the second exothermic peak, Nd9Fe81–xTi4C2Nb4Bx (x=11, 13, 15) bulk alloys obtained a finely mixed structure which were composed of Nd2Fe14B, α-Fe, Fe3B, (Nb,Ti)C crystalline phases and a residual amorphous phase, whose magnetic properties were significantly enhanced. For the bulk magnets of Nd9Fe81–xTi4C2Nb4Bx (x=11, 13, 15), the optimal magnetic properties of Br=0.63 T, iHc=155.1 kA/m, (BH)max=18.73 kJ/m3 could be achieved when x=13 after annealing at 983 K for 10 min.

Intrinsic relationship between crystallization mechanism of metallic glass powder and microstructure of bulk alloys fabricated by powder consolidation and crystallization of amorphous phase

Abstract Ti 64 Nb 12 Cu 11.2 Ni 9.6 Sn 3.2 bulk alloys were fabricated by consolidation of metallic glass (MG) powder synthesized by mechanical alloying and crystallization of amorphous phase. The Johnson–Mehl–Avrami–Kolmogorov method was employed to investigate non-isothermal crystallization kinetic of the synthesized MG powder. The average local Avrami exponent n determined from crystallization kinetic increases from 1.7 to 2.9 and then decreases to 1.8–2.0 when the crystallized volume fraction α is in the range of 0.1–0.3, and around 0.5 and 0.9, respectively. This indicates the corresponding crystallization mechanism is diffusion-controlled three-dimensional growth of nuclei with decreasing nucleation rate, volume diffusion-controlled three-dimension growth with increasing nucleation rate, and diffusion-controlled growth with decreasing nucleation rate, respectively. Meanwhile, the values of n imply that the nucleation rate increases with increasing heating rate. Microstructure analysis indicates that the fabricated bulk alloys mainly consist of three kinds of crystallized phases, β-Ti, (Cu, Ni)–Ti 2 , and Nb 3 Sn, but exhibit different microstructures and mechanical properties. The effect of the heating rate on the microstructure and mechanical properties can be explained based on different crystallization mechanisms. Especially, obvious plasticity is resulted from formation of ductile (Ti, Nb) 3 Sn from the Nb 3 Sn at relative high sintering temperature. The results obtained provide insight into fabrication of large-sized crystallized phase-containing bulk alloys with excellent mechanical property by powder metallurgy.

Effect of minor additions of Fe on bulk alloy microstructure and tensile properties of the low Ag‐content Sn‐1Ag‐0.5Cu solder alloy

PurposeThe purpose of this paper is to investigate the effects of small additions (0.1 and 0.3 wt%) of Fe on the bulk alloy microstructure and tensile properties of low Ag‐content Sn‐1Ag‐0.5Cu lead‐free solder alloy.Design/methodology/approachSn‐1Ag‐0.5Cu, Sn‐3Ag‐0.5Cu and Sn‐1Ag‐0.5Cu containing 1 and 3 wt.% Fe solder specimens were prepared by melting pure ingots of Sn, Ag, Cu and Fe in an induction furnace and subsequently remelting and casting to form flat dog‐bone shaped specimens for tensile testing. The solder specimens were subjected to tensile testing using an INSTRON tester with a loading rate 10‐3 s‐1. To obtain the microstructure, the solder samples were prepared by dicing, molding, grinding and polishing processes. The microstructural analysis was carried out using scanning electron microscopy/Energy Dispersive X‐ray spectroscopy. Electron backscatter diffraction (EBSD) analysis was used to identify the IMC phases.FindingsIn addition to large primary β‐Sn grains, the addition of Fe to the SAC105 alloy formed large circular shaped FeSn2 IMC particles located in the eutectic regions. This had a significant effect in reducing the elastic modulus and yield strength and maintaining the elongation at the SAC105 level. Moreover, the additions of Fe resulted in the inclusion of Fe in the Ag3Sn and Cu6Sn5 IMC particles. The additions of Fe did not have any significant effect on the melting behaviour.Research limitations/implicationsThe paper provides a starting‐point for studying the effect of minor additions of Fe on the drop impact and thermal cycling reliability of SAC105 alloy considering the bulk alloy microstructure and tensile properties. Further investigations should be undertaken in the future.Originality/valueThe effect of Fe addition on the bulk alloy microstructure and tensile properties of the SAC105 alloy has been studied for the first time. Fe‐containing SAC105 alloy may have the potential to increase the drop impact and thermal cycling reliability compared with the standard SAC105 alloy.

High-Reliability Low-Ag-Content Sn-Ag-Cu Solder Joints for Electronics Applications

Sn-Ag-Cu (SAC) alloy is currently recognized as the standard lead-free solder alloy for packaging of interconnects in the electronics industry, and high- Ag-content SAC alloys are the most popular choice. However, this choice has been encumbered by the fragility of the solder joints that has been observed in drop testing as well as the high cost of the Ag itself. Therefore, low-Ag-content SAC alloy was considered as a solution for both issues. However, this approach may compromise the thermal-cycling performance of the solders. Therefore, to enhance the thermal-cycling reliability of low-Ag-content SAC alloys without sacrificing their drop-impact performance, alloying elements such as Mn, Ce, Ti, Bi, In, Sb, Ni, Zn, Al, Fe, and Co were selected as additions to these alloys. However, research reports related to these modified SAC alloys are limited. To address this paucity, the present study reviews the effect of these minor alloying elements on the solder joint reliability of low-Ag-content SAC alloys in terms of thermal cycling and drop impact. Addition of Mn, Ce, Bi, and Ni to low-Ag-content SAC solder effectively improves the thermal-cycling reliability of joints without sacrificing the drop-impact performance. Taking into consideration the improvement in the bulk alloy microstructure and mechanical properties, wetting properties, and growth suppression of the interface intermetallic compound (IMC) layers, addition of Ti, In, Sb, Zn, Al, Fe, and Co to low-Ag-content SAC solder has the potential to improve the thermal-cycling reliability of joints without sacrificing the drop-impact performance. Consequently, further investigations of both thermal-cycling and drop reliability of these modified solder joints must be carried out in future work.

Microstructure and Tensile Properties of Sn-1Ag-0.5Cu Solder Alloy Bearing Al for Electronics Applications

This work investigates the effects of 0.1 wt.% and 0.5 wt.% Al additions on bulk alloy microstructure and tensile properties as well as on the thermal behavior of Sn-1Ag-0.5Cu (SAC105) lead-free solder alloy. The addition of 0.1 wt.% Al reduces the amount of Ag3Sn intermetallic compound (IMC) particles and leads to the formation of larger ternary Sn-Ag-Al IMC particles. However, the addition of 0.5 wt.% Al suppresses the formation of Ag3Sn IMC particles and leads to a large amount of fine Al-Ag IMC particles. Moreover, both 0.1 wt.% and 0.5 wt.% Al additions suppress the formation of Cu6Sn5 IMC particles and lead to the formation of larger Al-Cu IMC particles. The 0.1 wt.% Al-added solder shows a microstructure with coarse β-Sn dendrites. However, the addition of 0.5 wt.% Al has a great effect on suppressing the undercooling and refinement of the β-Sn dendrites. In addition to coarse β-Sn dendrites, the formation of large Sn-Ag-Al and Al-Cu IMC particles significantly reduces the elastic modulus and yield strength for the SAC105 alloy containing 0.1 wt.% Al. On the other hand, the fine β-Sn dendrite and the second-phase dispersion strengthening mechanism through the formation of fine Al-Ag IMC particles significantly increases the elastic modulus and yield strength of the SAC105 alloy containing 0.5 wt.% Al. Moreover, both 0.1 wt.% and 0.5 wt.% Al additions worsen the elongation. However, the reduction in elongation is much stronger, and brittle fracture occurs instead of ductile fracture, with 0.5 wt.% Al addition. The two additions of Al increase both solidus and liquidus temperatures. With 0.5 wt.% Al addition the pasty range is significantly reduced and the differential scanning calorimetry (DSC) endotherm curve gradually shifts from a dual to a single endothermic peak.

The bulk alloy microstructure and tensile properties of Sn‐1Ag‐0.5Cu‐xAl lead‐free solder alloys (x=0, 1, 1.5 and 2 wt.%)

PurposeThe purpose of this paper is to investigate the effect of Al addition on the bulk alloy microstructure and tensile properties of the low Ag‐content Sn‐1Ag‐0.5Cu (SAC105) solder alloy.Design/methodology/approachThe Sn‐1Ag‐0.5Cu‐xAl (x=0, 1, 1.5 and 2 wt.%) bulk solder specimens with flat dog‐bone shape were used for tensile testing in this work. The specimens were prepared by melting purity ingots of Sn, Ag, Cu and Al in an induction furnace. Subsequently, the molten alloys were poured into pre‐heated stainless steel molds, and the molds were naturally air‐cooled to room temperature. Finally, the molds were disassembled, and the dog‐bone samples were removed. The solder specimens were subjected to tensile testing on an INSTRON tester with loading rate 10−3 s−1. The microstructural analysis was carried out using scanning electron microscopy/Energy dispersive X‐ray spectroscopy. Electron Backscatter Diffraction (EBSD) analysis was used to identify the IMC phases. To obtain the microstructure, the solder samples were prepared by dicing, molding, grinding and polishing processes.FindingsThe addition of Al to the SAC105 solder alloy suppresses the formation of Ag3Sn and Cu6Sn5 IMC particles and leads to the formation of larger Al‐rich and Al‐Cu IMC particles and a large amount of fine Al‐Ag IMC particles. The addition of Al also leads to refining of the primary β‐Sn grains. The addition of Al results in a significant increase on the elastic modulus and yield strength. On the other hand, the addition of Al drastically deteriorates the total elongation.Originality/valueThe addition of Al to the low Ag‐content SAC105 solder alloy has been discussed for the first time. This work provides a starting‐point to study the effect of Al addition on the drop impact and thermal cycling reliability of the SAC105 alloy.

The bulk alloy microstructure and mechanical properties of Sn–1Ag–0.5Cu–xAl solders (x = 0, 0.1 and 0.2 wt. %)

This work investigates the effects of 0.1 and 0.2 wt. % Al additions on bulk alloy microstructure and tensile properties as well as on the thermal behavior of Sn–1Ag–0.5Cu (SAC105) lead-free solder alloy. The addition of Al reduces the amount of Ag3Sn intermetallic compound (IMC) particles and leads to the formation of larger Al–Ag IMC particles. Moreover, the addition of Al suppresses the formation of Cu6Sn5 IMC particles and leads to the formation of larger Al–Cu IMC particles. The Al added solders show a microstructure with large primary β-Sn grains. The tensile tests show that the 0.1 wt. % Al addition reduces the elastic modulus, yield strength and ultimate tensile strength (UTS). However, the 0.2 wt. % Al addition brings the yield strength up to SAC105 level and the UTS up to level slightly higher than that of SAC105, while its effect on reducing the elastic modulus becomes less dependent compared with the 0.1 wt. % Al addition. Moreover, both 0.1 and 0.2 wt. % Al additions deteriorate the total elongation. The two additions of Al slightly increase the solidus and liquids temperatures, while slightly reduce the pasty range, hence allowing the use of the Al-containing Sn–1Ag–0.5Cu alloys, to be consistent with the conditions of usage for conventional Sn–Ag–Cu solder alloys.

Precipitation in an AA6111 aluminium alloy and cosmetic corrosion

The near-surface deformed layer on AA6111 automotive closure sheet alloy, generated by mechanical grinding during rectification, has an ultrafine grain microstructure, of 50–150 nm diameter, and a sharp transition with the underlying bulk alloy microstructure. Grinding and heat treatment to simulate rectification and paint baking processes result in the nucleation and growth of ∼20 nm diameter precipitates at grain boundaries within the near-surface deformed layer. High-resolution transmission electron microscopy has shown Q phase precipitates in the deformed layer, giving dramatically increased corrosion susceptibility compared with the bulk microstructure, and this is responsible for the rapid-onset filiform corrosion. Transmission electron microscopy of the corrosion attack showed directly that the mode of corrosion was intergranular and that the Q phase precipitates were preserved after the passage of the corrosion front.

Production of ultrafine powders of BiSb solid solution

Investigations of the synthesis and consolidation of bismuth-antimony alloys submicrometric powders were performed. Powders containing from 6 to 20 atomic percent of antimony were prepared by evaporation of Bi-Sb pre-alloyed targets using arc energy under argon-hydrogen atmosphere. Chemical analyses, EDS analyses, morphological and microstructural studies were performed on the product powders. The influence of the evaporation parameters on the powder generation yield and the local chemical composition of the powders was studied. We show that the control of the powder permits adjustment in the powder particle size from 25 nm to 0.8 μm. Finally, we present the influence of the ultrafine powder morphology on the microstructure of bulk alloys prepared by cold pressing powders.