Bimodal Matrix Research Articles

Internal tensile properties of characteristic zones in the electron beam weldment of TC17 titanium alloy

The internal tensile deformation of the individual base metal zone (BM), heat-affected zone (HAZ), and fusion zone (FZ) in a titanium alloy (Ti–5Al–2Sn–2r–4Mo–4Cr, wt.%) electron beam welding (EBW) joint is investigated. The ultimate strength of BM with a bimodal microstructure is 1047.5 MPa, and the elongation to fracture is 9.8%. HAZ is distinguished by the formation of a ghost structure with a hierarchical cluster structure within the initial αP grains, while the embedded αs laths dissolve in the matrix and relatively coarsening β grains are generated. During tension, the ghost structures strongly inhibit and deflect slip initiation and extension in the relatively coarsening β matrix. The competitive balance between strengthening from the ghost structure and weakening from the coarsening matrix dominates the mechanical properties of the HAZ, which then induces a hybrid fracture. The needle-shaped thermal martensite that formed during EBW causes the FZ to fail prematurely. The microstructural evolution of HAZ and FZ decreases their mechanical properties. This research may shed some light on the mechanical enhancement of titanium alloys by utilizing the multiple αL laths precipitated within the initial αP structure associated with the bimodal matrix.

Decision Science Driven Selection of High-Temperature Conventional Ti Alloys for Aeroengines

Near-α Ti alloys find themselves in advanced aeroengines for applications of up to 600 °C, mainly as compressor components owing to their superior combination of ambient- and elevated-temperature mechanical properties and oxidation resistance. We evaluated, ranked, and selected near-α Ti alloys in the current literature for high-temperature applications in aeroengines driven by decision science by integrating multiple attribute decision making (MADM) and principal component analysis (PCA). A combination of 12 MADM methods ranked a list of 105 alloy variants based on the thermomechanical processing (TMP) conditions of 19 distinct near-α Ti alloys. PCA consolidated the ranks from various MADMs and identified top-ranked alloys for the intended applications as: Ti-6.7Al-1.9Sn-3.9Zr-4.6Mo-0.96W-0.23Si, Ti-4.8Al-2.2Sn-4.1Zr-2Mo-1.1Ge, Ti-6.6Al-1.75Sn-4.12Zr-1.91Mo-0.32W-0.1Si, Ti-4.9Al-2.3Sn-4.1Zr-2Mo-0.1Si-0.8Ge, Ti-4.8Al-2.3Sn-4.2Zr-2Mo, Ti-6.5Al-3Sn-4Hf-0.2Nb-0.4Mo-0.4Si-0.1B, Ti-5.8Al-4Sn-3.5Zr-0.7Mo-0.35Si-0.7Nb-0.06C, and Ti-6Al-3.5Sn-4.5Zr-2.0Ta-0.7Nb-0.5Mo-0.4Si. The alloys have the following metallurgical characteristics: bimodal matrix, aluminum equivalent preferably ~8, and nanocrystalline precipitates of Ti3Al, germanides, or silicides. The analyses, driven by decision science, make metallurgical sense and provide guidelines for developing next-generation commercial near-α Ti alloys. The investigation not only suggests potential replacement or substitute for existing alloys but also provides directions for improvement and development of titanium alloys over the current ones to push out some of the heavier alloys and thus help reduce the engine’s weight to gain advantage.

Synergistically enhanced strength and ductility of TiB/(TA15-Si) composites: A two-step HIP strategy

A novel two-step hot isostatic pressing strategy has been brought up to fabricate a kind of TiB/(TA15-Si) composites. The densification process and the process of introducing TiB reinforcement by in-situ synthesized reaction were separated. As a result, a network distribution of TiB reinforcement was achieved, and a bimodal matrix grain structure was regulated. By comparing the mechanical properties of the composites fabricated by traditional hot isostatic pressing method, we found that this novel strategy enhanced the yield strength and ultimate tensile strength by 9.6% and 11.0%, respectively. Moreover, the elongation was also improved from 4.7% to 6.6%. Through theoretical calculation and quasi-in-situ characterization, the strength enhancement was determined to be contributed by grain boundary strengthening, and the ductility was benefited by the bimodal structure of titanium matrix.

The chemistry of the extraterrestrial carbonaceous stone “Hypatia”: A perspective on dust heterogeneity in interstellar space

An extraterrestrial origin for a carbonaceous, diamond-bearing and silicate-free stone named “Hypatia”, found in 1996 in southwest Egypt, was determined in 2013 and confirmed in 2015 on the basis of argon, helium, neon, xenon and nitrogen isotope characteristics. Petrography and Raman spectroscopy has indicated that the parent body was primitive, i. e. not thermally processed in the solar nebula. Here we report the results of in situ chemical analyses of this object using proton induced X-ray emission (PIXE) spectroscopy. The stone has a bimodal matrix. Type 1 is essentially devoid of elements heavier than oxygen, whereas matrix 2 shows a unique, consistent element abundance pattern from aluminum to zinc, up to a sum of 4.5 wt%. Fe is dominant and Si markedly depleted, with a CI-chondrite normalized Si/Fe ratio of c. 0.1. Element abundance ratios to Fe show several correlations, with one group (Al, Si, K, Ca, Ti and Cu) being negatively correlated to another one (P, S and Ni). Since the parent body was primitive, magmatic differentiation cannot be invoked to account for any part of this dataset. Considering published Raman spectroscopic data and interstellar dust models, we hypothesize that Hypatia's parent body consisted of interstellar dust. However, Hypatia's matrix 2 chemistry does not fit predictions for the average interstellar dust composition based on absorption spectroscopic studies of element depletions in gas along stellar lines of sight. Instead, it shows similarities to the nucleosynthesis yields of specific supernova Ia models, whereby the element abundance correlations and the strong depletion of Si may be understood as resulting from nuclear photodisintegration. It has been known for decades that the chemistry of interstellar space is made up of many components, each bearing the signature of the nucleosynthesis processes giving rise to them. Now it appears from the case of Hypatia that an individual component was preserved in dust, and delivered to a region of the solar nebula where mixing did not obliterate it prior to the coagulation of larger bodies.

Microstructure formation in the powder HIPed hardfacing alloy Tristelle 5183 (Fe-21%Cr-10%Ni-7.5%Nb-5%Si-2%C in wt%)

Tristelle 5183 (Fe-21%Cr-10%Ni-7%Nb-5%Si-2%C in wt%) is an alternative material to cobalt-based alloys for wear resistant hardfacing applications. In this work, gas atomised powder was consolidated by hot isostatic pressing (HIPing) at 1120 ± 10 o C which is ∼ 100 o C below the melting onset point. The microstructure formation in the alloy, following densification, was investigated using X-ray diffraction, scanning and transmission electron microscopy and electron backscatter diffraction. The hot isostatically pressed (HIPed) alloy contains principally fcc γ -Fe, NbC, and M 7 C 3 with a small fraction of bcc α/δ -Fe and a π -ferrosilicide phase. This contrasts with the metastable gas atomised powder microstructure in which M 7 C 3 formation is largely suppressed and NbC precipitation is reduced. Following HIPing, a wide distribution of γ -Fe grain sizes is found. The larger grains exhibit sub-grain structures with significant intra-grain misorientations as identified by kernel average misorientation (KAM) maps. The smaller grains (< 10 μm) contain annealing twins, indicating that recrystallization had occurred only in certain localised regions which underwent sufficient plastic deformation in the early stages of HIPing. The work demonstrates the potential for HIPing hardfacing alloys to achieve a fine scale homogeneous microstructure. • HIPing homogenises the rapidly solidified powder microstructure of the alloy. • Insufficient recrystallisation of the powder results in a bimodal matrix grain size. • A mainly austenitic iron matrix contains NbC and M 7 C 3 precipitates. • M 7 C 3 is largely suppressed in the powder but precipitates out during HIPing.

Bowen-Franks Groups for Bimodal Matrices

From the symbolic description of iterated bimodal maps of the interval, we can associate such maps to square 0, 1 transition matrices, referred as bimodal matrices. We show that the Bowen-Franks group BF ( A ) of a bimodal matrix A is given Z c ] Z d , for some non-negative integers c , d .