Selective laser melting (SLM) involves periodic processes of rapid temperature rise and drop, so it is of great interest in evaluating the quality of the melted powders by real-time thermal information. In this study, a LumaSense MCS640 thermal imaging camera in coaxial system, which can track the location of melt pool, was used to real-time monitor the surface temperature during Ti-6Al-4V forming and predict an average melt width by extracting the boundary of the melt pool in each infrared image. The characteristics of the temperature gradient distribution around a melt pool instead of the temperature itself was analyzed, the boundary of a melt pool was determined then by the maximum (or minimum) temperature gradient point in space. Straight melt samples were obtained by a fixed laser scanning direction in this study, the extracted boundaries of the moving melt pool in the direction perpendicular to the laser scanning direction were compared with the measured melt width from a microscope. A best width divergency between the prediction and measurement around 5% is achieved.

We have calculated deposited energies of various energetic ions in carbon nanotubes, to study nuclear point mass effects, with the help of a static Monte Carlo (MC) simulation program. As a result of nuclear point mass effects, we show that at the same incident energy, the ion-deposited energy maximizes, while its mass has intermediate mass values, such as 11 B, 12 C and 14 N ion masses, under hundreds keV 4 He, 11 B, 12 C, 14 N, 20 Ne, 28 Si and 40 Ar ion irradiations of a thin-walled carbon nanotube. We also show that at the same incident energy, the coordination defect number maximizes, while its mass has an intermediate mass ( 20 Ne) value, under hundreds keV 4 He, 20 Ne and 40 Ar ion irradiations of the thin-walled nanotube. We derive an ion-deposited energy formula to analyze these maximum phenomena, and compare the MC simulation results with the MD (molecular dynamics) ones.

The channeling phenomenon of carbon ions in single-wall carbon nanotubes (SWCNTs) is investigated by using the molecular dynamics simulation with analytical potentials. The relationship between the channeling critical angles in the SWCNT and the bonding interaction is analyzed. It was found that, at 200-5000 eV and 10 degrees-20 degrees of incident angle, the ions with the bonding interaction or chemical effect, have decreased dechanneling probabilities and increased critical angles, compared to that of non-bonding ions. So the bonding effect cannot be ignored in the channeling mechanism of carbon ions through a SWCNT.

In April, 2010, after reading "An improved critical angle equation for ion channeling" (Zheng theory) proposed by Zheng et al. (1) in Nuclear Instruments and Methods in Physics Research Section B (NIM-B), we felt very strange, because the theory contradicts the well-known Lindhard theory (2) and many of the experimental results published during the last few decades (3). Therefore, we submitted our first comments (4) to NIM-B for publication on 15 April 2010. In September 2010, we had found a new paper published by Zheng et al. (5) in Radiation Effects and Defects in Solids. In the latter paper (5), Zheng et al. studied the isotopic mass effects for low-energy channeling in a silicon crystal by using Monte Carlo (MC) simulations. Immediately, we remembered that a similar work had been published by Zheng et al. two years before for low-energy ion channeling in single-wall carbon nanotubes (SWCNT) (6). The aim of the two papers (5, 6) is finding simulation evidence to support the Zheng theory (1) by studying isotopic ion channeling.

[Zheng, Li-Ping; Zhu, Zhi-Yuan; Li, Yong] Chinese Acad Sci, Shanghai Inst Appl Phys, Shanghai 201800, Peoples R China. [Zheng, Li-Ping] Chinese Acad Sci, Int Ctr Mat Phys, Shenyang 110016, Peoples R China. [Goodman, Frank O.] Univ Waterloo, Dept Appl Math, Waterloo, ON N2L 3G1, Canada.;Li, Y (reprint author), Chinese Acad Sci, Shanghai Inst Appl Phys, POB 800-204, Shanghai 201800, Peoples R China;liyong@sinap.ac.cn

[zheng, li-ping; zhu, zhi-yuan; li, yong; yan, long] chinese acad sci, shanghai inst appl phys, shanghai 201800, peoples r china. [zheng, li-ping] chinese acad sci, int ctr mat phys, shenyang 110016, peoples r china.;li, y (reprint author), chinese acad sci, shanghai inst appl phys, pob 800 204, shanghai 201800, peoples r china;liyong@sinap.ac.cn

Channeling phenomena of He, Ne, Ar and Kr ions at energy (200-5000 eV) in single-wall carbon nanotubes (SWCNTs) are investigated by molecular dynamics simulation with analytical potentials. The critical angles for the particles to be channeled in an SWCNT are analyzed. In the incident energy range of 200-5000 eV, it is found that the ion energy dependence of the critical angle obeys an improved Lindhard equation which is closely related to the ratio of nuclear charge number to atomic mass Z/M. The critical angle for different types of ions channeling in SWCNTs is determined by both the atomic nuclear charge and mass.

Lindhard proposed his classical equation for the critical channeling angle from consideration of conservation of transverse energy. We generalize those ideas via consideration of conservation of transverse momentum, and propose an improved equation. A dimensional analysis of the problem is also presented, and that analysis puts our arguments and results on a firm footing.

We have developed a mass- and charge-dependent equation to predict theoretical critical angles for ion channeling in carbon nanotubes. We focus M (ion mass) effects how to reduce Ze (ion nucleus charge) effects on ΨC (critical angles). As an instance, we give theoretical critical angels of He, Ne, Ar, Kr, Xe and Rn ion channeling in carbon nanotubes. We find that for (10,10) single-wall carbon nanotubes, ΨC(He)≈ΨC(Ne)≈ΨC(Ar)≈ΨC(Kr)≈ΨC(Xe)≈ΨC(Rn)≈23.3(keV/E)1/2deg. This is because (Z/M)1/2≈0.66[amu]−1/2.

An Monte Carlo (MC) simulation program has been used to study ion mass dependence for the low energy channeling of natural- and pseudo-Ar ions in single-wall nanotubes. The MC simulations show that the channeling critical angle ΨC obeys the (E)−1/2 and the (M1)−1/2 rules, where E is the incident energy and M1 is the ion mass. The reason for this may be that the motion of the channeled (or de-channeled) ions should be correlated with both the incident energy E and the incident momentum (2M1E)1/2, in order to obey the conservation of energy and momentum.

Monte Carlo (MC) simulation studies of isotopic mass effects have been conducted, for low-energy channeling of C-12 and C-13 ions in single-wall carbon nanotubes. It is found in MC simulations that (Psi(C) (for) C-12/Psi(C) (for) C-13) = (13/12)(1/2), for the same incident energies. Here, Psi(C) (for) C-12 is the critical angle for C-12 channeling, and Psi(C) (for) C-13 is the critical angle for C-13 channeling. This work shows the mass effect to be the incident momentum one, but a recent work (Moura, C. S.; Amaral, L. J. Phys. Chem. B 2005, 109, 13515) considered it to be the energy transfer effect. Our work disagrees with that of Moura and Amaral.

For high-energy particle transmission,its mass depends on its incident energy.For low-energy particle transmission,its (static) mass is independent of its incident energy.The difference between the mass ideas is rather than that between high and low energies.Thus,these two transmission studies are very different in ideas.The column symmetry of transverse continuum potential well is independent of the nanotube structure.X-ray transmission consists of two aspects:as wave,it is scattered by the laws of ray optics;as particle,it is captured in the transverse continuum potential well.

Recently, a new capillary optics focus element, which is composed of many bent-multi-walled nanotubes, can be used to produce the high strength nanometer-X-ray beams. In the world, as new elements of diffraction propagation of X-ray, the single-walled nanotubes (rope) and the fullerites (C60 crystal) have caused great interest in the world. This paper introduces the progress of the above studied field.

The dual-species model is based on the Monte Carlo simulation conjoined with the embedded atom method (EAM) potentials. The model suggests that during relaxation of Ni3Al grain boundary，the trace element atoms can be seen not only as segregating species but also as inducing species. As segregating species the trace element atoms segregate (or enrich) to the grain boundary, but as inducing species they induce Ni atoms to segregate (or enrich) to the grain boundary. Evidently, the model can explain why the trace element atoms and Ni atoms co-segregate (or co-enrich) to the grain boundary. According to combination of positive (as inducing species) and negative (as segregating species) effects, the model explains the most obvious Ni-enrichment phenomenon at Ni3Al grain boundaries.

The Monte Carlo simulation program has been used to study low energy channeling in the single-wall nanotube and its rope, in comparisons between beam sizes and between light (He) and heavy (Ar) ions. The simulation mainly shows that the critical angle ΨC=48E−1/2 (E is incident energy) for the He (light) ion channeling but ΨC=18E−1/2 for the Ar (heavy) ion channeling, in the (17,0) zigzag single-wall nanotube. Thus, it might be found in the simulation that ΨC strongly depends on the ion mass.

Monte Carlo simulation is used to study the low energy He ion challenging in a (17,0) single-wall nanotube and its rope. The simulation shows that the channelling critical angle Psi(C) = 48E(-1/2) (E is incident energy) for a 1.31-nm-diameter initial beam into the nanotube, while Psi(C) = 45E(-1/2) for the 1.31-nm-diameter initial beam into its rope.

Monte Carlo simulation with the energetics described by the embedded atom method has been employed to calculate dependence of the grain boundary cohesion on the Zr bulk atom concentration, for the Ni_3Al-x % Zr (100%Ni\\100%Ni)\/Σ5(210)/36.87° symmetric tilt grain boundary, at the equilibrium. Calculations show that when x (the Zr bulk atom concentration) increases from 0.1 to 0.5, the Zr enrichment increases, both the Ni enrichment and the Al depletion maximizes at x=0.3. The calculations also show the best cohesion of the grain boundary at (x=0.3).

Based on the Monte Carlo simulation conjoined with the embedded atom method (EAM) potentials, a double species model is employed to study the Ni75-3x/4Al25-x/4Crx (x < 3) structure, i.e. impure Ni3Al together with a grain boundary structure at the equilibrium. At the grain boundary, the model shows that Ll(2)-Ni3Al transforms into fcc-Ni when x increases from 0 to 0.40; then fcc-Ni transforms into Ll(2)-Ni3Cr when x increases from 0.40 to 2.40.