Freeform Fabrication of Ti3SiC2 Structures

This paper introduces a three-stage process to fabricate highly dense Ti3SiC2 structures. The properties of Ti3SiC2 material, the synthesis of the ceramic powder, the procedure involved in the 3-stage fabrication process and the preliminary results on fabricating fully dense Ti3SiC2 structures are presented. The characterization and microstructure evaluation of the mechanical, morphological and structural properties covering the compressive strength, Vickers micro hardness, damage tolerance, thermal shock, shrinkage and porosity of Ti3SiC2 structures printed using the 3-stage process are presented.Mechanical Engineerin

Ta2AlC and Cr2AlC Ag-based composites-New solid lubricant materials for use over a wide temperature range against Ni-based superalloys and alumina

Wear, 262(11): pp. 1479-1489.The tribological performances of the two new composite materials, consisting of the layered ternary carbides (MAX phases), Ta2AlC or Cr2AlC, and 20 vol.% Ag, were investigated in the temperature range from ambient to 550 ◦C against a Ni-based superalloy, SA (Inconel 718) and alumina counterparts. Over the entire temperature range, the wear rates, WRs, during dry sliding against the SA counterparts for the Ta2AlC–Ag and Cr2AlC–Ag composites were <5×10−5 and <10−4 mm3/Nm, respectively. The friction coefficients, μ, were <0.5. The WRs of the SA counterparts were also relatively low (<10−4 mm3/Nm). Under thermocycling conditions, the tribological performance of the MAX/Ag composites-Inc718 tribocouples got better with sliding distance. When the composites were tested against Al2O3, their WRs at moderate temperatures were also ≈10−5 mm3/Nm, but at 550 ◦CtheWRsincreased by about an order or magnitude. Both composites had tensile strengths, σt, >150MPa, compressive strengths, σc, >1.5 GPa at ambient temperature and σt > 100MPa at 550 ◦C. Their good tribological performance together with decent mechanical properties and machinability render them promising materials for various high temperature tribological applications

Electrical transport, thermal transport, and elastic properties of M2AlC (M=Ti, Cr, Nb, and V)

Physical Review B: Condensed Matter and Materials Physics, 72(11): pp. 115120-1—115120-6. Retrieved September 19, 2006 from http://www.mse.drexel.edu/max/pdf%20references/drexel_pdfs/papers/2005/HettingerPRB%202005_NSF.pdf. DOI: http://dx.doi.org/10.1103/PhysRevB.72.115120In this paper we report on a systematic investigation, in the 5 to 300 K temperature regime, of the electronic, magnetotransport, thermoelectric, thermal, and elastic properties of four M2AlC phases: Ti2AlC, V2AlC, Cr2AlC, and Nb2AlC. The electrical conductivity, Hall coefficient, and magnetoresistances are analyzed within a two-band framework assuming a temperature-independent charge carrier concentration. As with other MAX-phase materials, these ternaries are nearly compensated, viz. the densities and mobilities of electrons and holes are almost equal. There is little correlation between the Seebeck and Hall coefficients. With Young’s and shear moduli in the 270 GPa and 120 GPa range, respectively, the phases studied herein are reasonably stiff. With room temperature thermal conductivities in the 25 W/m K range (45 W/m K for V2AlC) they are also good thermal conductors

Synthesis and DFT investigation of new bismuth-containing MAX phases

The M(n + 1)AX(n) phases (M = early transition metal; A = group A element and X = C and N) are materials exhibiting many important metallic and ceramic properties. In the present study powder processing experiments and density functional theory calculations are employed in parallel to examine formation of Zr(2)(Al(1−x)Bi(x))C (0 ≤ x ≤ 1). Here we show that Zr(2)(Al(1−x)Bi(x))C, and particularly with x ≈ 0.58, can be formed from powders even though the end members Zr(2)BiC and Zr(2)AlC seemingly cannot. This represents a significant extension of the MAX phase family, as this is the first report of a bismuth-based MAX phase

Processing and characterization of Ti2AlC, Ti2AlN, and Ti2AlC0.5N0.5

In this article, we report on the fabrication and characterization of Ti2AlC, Ti2AlN, and Ti2AlC0.5N0.5. Reactive hot isostatic pressing (hipping) at ≈40 MPa of the appropriate mixtures of Ti, Al4C3 graphite, and/or AlN powders for 15 hours at 1300°C yields predominantly single-phase samples of Ti2AlC0.5N0.5; 30 hours at 1300°C yields predominantly single-phase samples of Ti2AlC. Despite our best efforts, samples of Ti2AlN (hot isostatic pressed (hipped) at 1400°C for 48 hours) contain anywhere between 10 and 15 vol pct of ancillary phases. At ≈25 μm, the average grain sizes of Ti2AlC0.5N0.5 and Ti2AlC are comparable and are significantly smaller than those of Ti2AlN, at ≈100 μm. All samples are fully dense and readily machinable. The room-temperature deformation under compression of the end-members is noncatastrophic or graceful. At room temperature, solid-solution strengthening is observed; Ti2AlC0.5N0.5 is stronger in compression, harder, and more brittle than the end-members. Conversely, at temperatures greater than 1200°C, a solid-solution softening effect is occurring. The thermal-expansion coefficients (CTEs) of Ti2AlC, Ti2AlN, and Ti2AlC0.5N0.5 are, respectively, 8.2 × 10-6, 8.8 × 10-6, and 10.5 × 10-6 °C-1, in the temperature range from 25°C to 1300°C. The former two values are in good agreement with the CTEs determined from high-temperature X-ray diffraction (XRD). The electrical conductivity of the solid solution (3.1 × 106 (Ω m)-1) is in between those of Ti2AlC and Ti2AlN, which are 2.7 × 106 and 4.0 × 106 Ω-1 m-1, respectively