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MAX-phases are hexagonal ternary carbides and nitrides with the general formula: M
n + 1
AX
n
and n = 1 to 3. 111In was implanted into the two MAX compounds Ti2InC and Zr2InC. Based on the general knowledge of previous 111In implantations one expects to find the probes on the indium lattice-site in these compounds. First experiments on the anneal...
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... (ν Q = 17 MHz, η = 0). Above the indium melting point we found f In = 65% with ν Q = 0 MHz, a clear proof, that the 111 In is located in metallic indium. The rest of the probes showed two well defined EFGs of similar magnitude, fitted with the parameters ν Q1 = 348 MHz, ν Q2 = 328 MHz and η 1 = η 2 = 0 (see Table 1). The PAC-spectra are given in Fig. 4. The temperature and annealing conditions are included in the same figure. Similarly to the case of Ti 2 InC we attribute this high frequency to probes on the In-lattice site of Zr 2 InC. ...
Citations
... Jeitschko et al. [13] prepared Ti 2 InC for the first time by treating Ti/In/TiC in a sealed ampoule at 850°C for 350 h. By sintering a stoichiometric Ti/In/C powder mixture via hot isostatic pressing (HIP) at 1300°C for 7 h, Barsoum et al. [8] successfully synthesized dense Ti 2 InC bulks with~5 vol.% impurity phase of In, and this method has been widely used in the studies of Ti 2 InC [11,12,14]. Cuskelly [15] pioneered the preparation of Ti 2 InC by pressureless sintering method, and the preparation process required sintering a stoichiometric Ti/In/C compressed block at 1300°C for 7 h, obtaining a conversion of 85 wt% with 11 wt% of TiC and 4wt% of In. ...
Ti2InC is expected to have promising applications in many fields owing to its excellent conductivity and stability, and large-scale synthesis of high-quality Ti2InC is crucial to explore its various potential applications. In this paper, Ti2InC powder is synthesized starting from elemental Ti/In/C powder mixtures by pressureless sintering. Composition of starting powder and sintering parameters are optimized for synthesizing Ti2InC. Ti2InC phase can be obtained facilely by sintering a mixture of 2Ti/1In/0.95C (molar ratio) at 1250 °C for 1.5 h, which greatly shortens the preparation time. The purity of the Ti2InC in the sintered product reaches 94 wt%, evaluated by the relative intensity ratio (RIR) method analysis, and unreacted C is confirmed as a major impurity phase. The reaction path of Ti2InC formation is revealed by DSC, XRD, and SEM, and the formation mechanism of Ti2InC is discussed. A novel discovery is that TiC is not formed during the synthesis of Ti2InC.
... This kind of cross-section has previously been observed in the e.g. MAXphases [48] and in the W 2 B 5 phase [2] and is expected for a nanolaminated material where the bond strengths between the nanolaminated slabs are relatively weak. EDS analyses of the grains showing this behaviour confirmed the 1:2 stoichiometry of the Al:M ratio in the bulk sample. ...
Combining theory with experiments, we study the phase stability, elastic properties, electronic structure and hardness of layered ternary borides AlCr2B2, AlMn2B2, AlFe2B2, AlCo2B2, and AlNi2B2. We find that the first three borides of this series are stable phases, while AlCo2B2 and AlNi2B2 are metastable. We show that the elasticity increases in the boride series, and predict that AlCr2B2, AlMn2B2, and AlFe2B2 are more brittle, while AlCo2B2 and AlNi2B2 are more ductile. We propose that the elasticity of AlFe2B2 can be improved by alloying it with cobalt or nickel, or a combination of them. We present evidence that these ternary borides represent nanolaminated systems. Based on SEM measurements, we demonstrate that they exhibit the delamination phenomena, which leads to a reduced hardness compared to transition metal mono- and diborides. We discuss the background of delamination by analyzing chemical bonding and theoretical work of separation in these borides.
... Previous work on MAX phases, using PAC with an 111 In-111 Cd probe, revealed the existence of A site specific, strong, and axially symmetric EFGs in In, Al, Ge, and As containing 211-MAX phases [22][23][24]. Based on those results, it is now possible to investigate the deformation of polycrystalline MAX phases by an experiment, in which PAC spectra, measured under uniaxial load and after removing the load, are compared. ...
... Slight deviations from an ideal EFG give rise to an attenuation of R(t). The assumption of a distribution in only V zz [35] leads to the widely used expression for the perturbation function of a single fraction of probe surroundings with the distribution width δ, the amplitudes s 2n and coefficients g n depending solely on η [33,34], and the anisotropy of the γ-γ-cascade A 22 . For a = 1, Lorentzian, and for a = 2, Gaussian distributions are obtained. ...
We use the perturbed angular correlation method with (111)In-(111)Cd probe atoms to in situ study the changes in the electric field gradient at room temperature of polycrystalline Ti2AlN and Nb2AlC, titanium and zinc, and rutile samples, as a function of cyclic uniaxial compressive loads. The load dependence of the quadrupole coupling constant νQ was found to be large in titanium and zinc but small in Ti2AlN, Nb2AlC and rutile. Reversible and irreversible increases in the electric field gradient distribution widths were found under load and after releasing the load, respectively. Annihilation of dislocations, as well as elastic deformation, are considered to contribute to the reversible behavior. The irreversible response must be caused by a permanent increase in dislocation and point defect densities. The deformation induced broadening of the electric field gradient can be recovered by post-annealing of the deformed sample.
... For some MAX phases this question can easily be answered by choosing the compounds which have indium as a constituent. Owing to that consideration, previous experiments were performed for the key-compounds Ti 2 InC and Zr 2 InC [10] since the A-element is chemically identical to the 111 In atoms. One expects that the probes occupy the In-site or more generally the A-site. ...
... Simply speaking, one gets a ''fingerprint" of a certain lattice site. We found in [10] that these phases show, after long annealings at high temperatures, axially symmetric EFGs with quadupole coupling con- Using 111 In in other 211-phases which do not contain indium as a constituent, one expects an EFG in the same range of about 300 MHz assuming 111 In atoms at A-sites. The purpose of this work is to characterize the A-site EFG parameters for 111 In incorporated in the compounds Ti 2 AlN and Cr 2 GeC and to study the annealing behavior after implantation of In probe atoms. ...
... Above 1000 K more than 25% of the still present 111 In probes were lost from the samples, reaching a maximum value of 45-65% at 1273 K depending on the annealing duration. Previous studies of indium containing MAX phases have shown that the loss occured by the precipitation of excessive indium [10]. ...
PAC measurements were done for the first time on the 211-MAX phases Ti 2 AlN and Cr 2 GeC which do not have indium as a constituent material. Radioactive 111 In + ions were implanted at 400 keV into the MAX bulk-samples. The radiation damage was annealed under vacuum up to temperatures of 1373 K. During each heating cycle the samples were sealed in new quartz tubes, as a loss of the 111 In probes out of the samples was observed at high temperatures. Both MAX phases showed EFGs similar to the ones observed in indium containing MAX phases. In all cases they are attributed to probes residing on the A-site of the 211-structure. After high and long annealing temperatures an additional fraction of probes is observed in Cr 2 GeC with a different EFG. The corresponding site may be the M-site of the 211-structure, or a site in Cr 2 C. The comparison of the X-ray diffraction spectra, taken before the implantation and after the end of the PAC measurements, showed that Cr 2 GeC partly disintegrates to Cr 2 C.
Introduction Response of Quasi-Single Crystals to Compressive Loads Response of Polycrystalline Samples to Compressive Stresses Response of Polycrystalline Samples to Shear Stresses Response of Polycrystalline Samples to Flexure Stresses Response of Polycrystalline Samples to Tensile Stresses Hardness Fracture Toughness and R-Curve Behavior Fatigue Resistance Damage Tolerance Micromechanisms Responsible for High K1c, R-Curve Behavior, and Fatigue Response Thermal Sock Resistance Strain Rate Effects Solid Solution Hardening and Softening Machinability Summary and Conclusions References
The method of perturbed angular correlation (PAC) was applied to selected MAX phases with 211 stoichiometry. Radioactive 111In ions were implanted in order to measure the electric field gradients (EFG) in the key compounds Ti2InC and Zr2InC to determine the strength and symmetry of the EFG at the In-site. Further PAC studies in the In-free MAX phases Ti2AlN, Nb2AlC, Nb2AsC and Cr2GeC were performed to confirm that the In probes occupy the A-site as well. The strength of the EFG, with a quadrupole coupling constant νQ between 250 and 300 MHz in these phases, is quite similar to the ones found in Ti2InC with νQ = 292(1) MHz and in Zr2InC with νQ = 344(1) MHz, respectively. Different annealing behavior was observed whereas in all cases a linear decrease of νQ with increasing measuring temperatures was found. The experimental results are also in excellent agreement with those predicted by ab initio calculations using the APW+lo method implemented in the WIEN2k code. This study shows in an exceptional manner that 111In → 111Cd atoms are suitable probes to investigate the local surrounding at the A-site in 211-MAX phases.
PAC measurements were done for the first time on the 211-MAX phases Ti2AlN and Cr2GeC which do not have indium as a constituent material. Radioactive 111In+ ions were implanted at 400 keV into the MAX bulk-samples. The radiation damage was annealed under vacuum up to temperatures of 1373 K. During each heating cycle the samples were sealed in new quartz tubes, as a loss of the 111In probes out of the samples was observed at high temperatures. Both MAX phases showed EFGs similar to the ones observed in indium containing MAX phases. In all cases they are attributed to probes residing on the A-site of the 211-structure. After high and long annealing temperatures an additional fraction of probes is observed in Cr2GeC with a different EFG. The corresponding site may be the M-site of the 211-structure, or a site in Cr2C. The comparison of the X-ray diffraction spectra, taken before the implantation and after the end of the PAC measurements, showed that Cr2GeC partly disintegrates to Cr2C.