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Item type:Publication, Access status: without files , Laser additive manufacturing of ultrafine TiC particle reinforced Inconel 625 based composite parts: Tailored microstructures and enhanced performanceLaser metal deposition (LMD) additive manufacturing process was applied to produce ultrafine TiC particle reinforced Inconel 625 composite parts. The effects of laser energy input per unit length (LEIPUL) on microstructure development, densification response, and mechanical performance including wear performance and tensile properties were comprehensively studied. A relationship of processing conditions, microstructural characteristics, mechanical performance, and underlying strengthening mechanisms was proposed for a successful LMD of high-performance Inconel based composite parts. It revealed that using an insufficient LEIPUL of 33kJ/m lowered the densification behavior of LMD-processed parts, due to the appearance of residual large-sized pores in inter-layer areas of the parts. An increase in LEIPUL above 100kJ/m yielded the near fully dense composite parts after LMD. On increasing LEIPUL, the TiC reinforcing particles became significantly refined and smoothened via the elevated melting of particle surfaces and the dispersion state of ultra-fine reinforcing particles was homogenized due to the efficient action of Marangoni flow within the molten pool. The dendrites of Ni-Cr γ matrix underwent a successive change from an insufficiently developed, disordered microstructure to a refined, ordered microstructure with the increase of LEIPUL. However, the columnar dendrites of the matrix were coarsened apparently at an excessive LEIPUL of 160kJ/m because of the elevated thermalization of the input laser energy. The formation of the refined columnar dendrites of Ni-Cr γ matrix combined with the homogeneously distributed ultra-fine reinforcing particles contributed to the enhancement of wear performance of LMD-processed composites with a considerably low coefficient of friction (COF) of 0.30 and reduced wear rate of 1.3×10-4mm3/Nm. The optimally prepared TiC/Inconel 625 composite parts demonstrated a ductile fracture mode with a sufficiently high tensile strength of 1077.3MPa, yield strength of 659.3MPa, and elongation of 20.7%. The superior tensile properties of LMD-processed parts were attributed to the significant grain refinement effect of the matrix during laser processing and the efficient prohibition of ultrafine reinforcing particles on the mobility of dislocations.Publicationtype: Journal Article21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Densification behavior, microstructure evolution, and wear property of TiC nanoparticle reinforced AlSi10Mg bulk-form nanocomposites prepared by selective laser melting(Laser Inst. of America, 2014-12-09); ; ; ; Selective laser melting (SLM), due to its unique additive manufacturing processing philosophy, demonstrates a high potential in producing bulk-form nanocomposites with novel nanostructures and enhanced properties. In this study, the nanoscale TiC particle reinforced AlSi10Mg nanocomposite parts were produced by SLM process. The influence of "laser energy per unit length" (LEPUL) on densification behavior, microstructural evolution, and wear property of SLM-processed nanocomposites was studied. It showed that using an insufficient LEPUL of 250-J/m lowered the SLM densification due to the balling effect and the formation of residual pores. The highest densification level (>98% theoretical density) was achieved for SLM-processed parts processed at the LEPUL of 700-J/m. The TiC reinforcement in SLM-processed parts experienced a structural change from the standard nanoscale particle morphology (the average size 75-92-nm) to the relatively coarsened submicron structure (the mean particle size 161-nm) as the applied LEPUL increased. The nanostructured TiC reinforcement was generally maintained within a wide range of LEPUL from 250 to 700-J/m and the dispersion state of nanoscale TiC reinforcement was homogenized with increasing LEPUL. The sufficiently high densification rate combined with the uniform distribution of nanoscale TiC reinforcement throughout the matrix led to the considerably low coefficient of friction of 0.38 and wear rate of 2.76-×-10-5 mm3 N-1 m-1 for SLM-processed nanocomposites at 700-J/m. Both the insufficient SLM densification response at a relatively low LEPUL of 250-J/m and the disappearance of nanoscale reinforcement at a high LEPUL of 1000-J/m lowered the wear performance of SLM-processed nanocomposite parts.Publicationtype: Journal Article27 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , High-temperature oxidation performance and its mechanism of TiC/Inconel 625 composites prepared by laser metal deposition additive manufacturing(Laser Inst. of America, 2014-12-09); ; ; ; The laser metal deposition (LMD) additive manufacturing process was applied to produce TiC/Inconel 625 composite parts. The high-temperature oxidation performance of the LMD-processed parts and the underlying physical/chemical mechanisms were systematically studied. The incorporation of the TiC reinforcement in the Inconel 625 improved the oxidation resistance of the LMD-processed parts, and the improvement function became more significant with increasing the TiC addition from 2.5-wt. % to 5.0-wt. %. The mass gain after 100-h oxidation at 800-°C decreased from 1.4130-mg/cm2 for the LMD-processed Inconel 625 to 0.3233-mg/cm2 for the LMD-processed Inconel 625/5.0-wt. % TiC composites. The oxidized surface of the LMD-processed Inconel 625 parts was mainly consisted of Cr2O3. For the LMD-processed TiC/Inconel 625 composites, the oxidized surface was composed of Cr2O3 and TiO2. The incorporation of the TiC reinforcing particles favored the inherent grain refinement in the LMD-processed composites and, therefore, the composite parts possessed the sound surface integrity after oxidation compared with the Inconel 625 parts under the same oxidation conditions. The LMD-processed TiC/Inconel 625 composites exhibited the excellent oxidation resistance under the oxidation temperature of 800-°C. A further increase in the oxidation temperature to 1000-°C caused the severe oxidation attack on the composites, due to the unfavorable further oxidation of Cr2O3 to CrO3 at the elevated treatment temperatures.Publicationtype: Journal Article20 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Laser additive manufacturing LAM - fundamentals of selective laser melting SLM and laser material deposition LMD(Optical Society of America (OSA), 2014-06); ; With Additive Manufacturing AM, parts can be manufactured for design instead of being designed for manufacture. This tutorial introduces the two laser based AM processes, Selective Laser Melting SLM and Laser Material Deposition LMD.Publicationtype: Conference Paper26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fabrication of nano-TiCp reinforced Inconel 625 composite coatings by partial dissolution of micro-TiCp through laser cladding energy input controlNano-particulate reinforced metal matrix composites (nPRMMCs) exhibit excellent comprehensive properties unmatched by conventional micro-particulate reinforced metal matrix composites (μPRMMCs). However, current techniques for fabricating nPRMMCs usually use nano-powders as raw materials, which are not preferred due to their agglomeration trend and harmful size. In this paper, we developed a technique to fabricate nano-TiCp reinforced Inconel 625 composite coatings by laser cladding of an Inconel 625+5wt.% TiC powder mixture, particle size of the raw powders both in micrometer range. By controlling the specific energy input, the micro-TiCp partially dissolved into nanometer scale. The influence of specific energy input on particle size, morphology and the microstructure, phase constitution and mechanical properties of the composite coatings were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and nano-indentation test. Nano-TiCp reinforced Inconel 625 composite coatings were achieved at the specific energy input of 25.3kJ/g. The hardness and modulus of the nPRMMCs are 3.36GPa and 190.91GPa, increased by 10.33% and 12.39% respectively compared to laser cladded Inconel 625 substrate. The nPRMMCs show potential in applications such as the fabrication of turbine blades and engine components with improved performance.Publicationtype: Journal Article25 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Combined strengthening of multi-phase and graded interface in laser additive manufactured TiC/Inconel 718 compositesLaser metal deposition (LMD) additive manufacturing of TiC particle reinforced Inconel 718 composite parts was performed. The influence of laser energy density (LED) on densification, microstructures and wear behaviour of LMD-processed composites was studied. It showed that using a LED of 280 J mm-3 produced ∼5% porosity in LMD-processed composites, caused by the aggregation of reinforcing particles. A further increase in LED above 350 J mm-3 yielded near-full densification. Two categories of reinforcing phases, i.e. the substoichiometric TiCx particles and the in situ (Ti,M)C (M = Mo, Nb and Cr) carbide having 7-10 at% Nb and Mo contents, were formed in the matrix of LMD-processed composites. The TiCx reinforcing particles changed from an irregular poly-angular shape to a smoothened and refined structure as the LED increased. An increase in LED resulted in a larger amount of phase formation and an enhanced degree of crystal growth of the in situ (Ti,M)C reinforcement. The interfacial graded layer with thickness of 0.2-1.2 μm, which was identified as (Ti,M)C (M = Mo, Nb and Cr) carbide with 5-6 at% Mo and Nb contents, was tailored between the TiC x particles and the matrix. At an optimal LED of 420 J mm -3, a considerably low coefficient of friction of 0.38 and resultant low wear rate of 1.8 × 10-4 mm3 N-1 m-1 were obtained in sliding tests, due to the combined strengthening of the interfacial graded layer and the multiple reinforcing phases. The wear resistance decreased at an excessive LED because of the coarsening of reinforcement crystals and the decrease in microstructural uniformity of composites.Publicationtype: Journal Article22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Laser metal deposition of TiC/Inconel 718 composites with tailored interfacial microstructuresLaser metal deposition (LMD) was applied to deposit Inconel 718 metal matrix composites reinforced with TiC particles. The influence of laser energy input per unit length on constitution phases, microstructures, hardness, and wear performance of LMD-processed TiC/Inconel 718 composites was studied. It revealed that the LMD-processed composites consisted of γ Ni-Cr solid solution matrix, the intermetallic precipitation phase γ′, and the TiC reinforcing phase. For the laser energy input per unit length of 80-120 kJ/m, a coherent interfacial layer with the thickness of 0.8-1.4 μm was formed between TiC reinforcing particles and the matrix, which was identified as (Ti,M)C (M=Nb and Mo) layer. Its formation was due to the reaction of the strong carbide-forming elements Nb and Mo of the matrix with the dissolved Ti and C on the surface of TiC particles. The microstructures of the TiC reinforcing phase experienced a successive change as laser energy input per unit length increased: Relatively coarsened poly-angular particles (80 kJ/m) - surface melted, smoothened TiC particles (≥100 kJ/m) - fully melted/precipitated, significantly refined TiC dendrites/particles (160 kJ/m). Using the laser energy input per unit length ≥100 kJ/m produced the fully dense composites having the uniformly dispersed TiC reinforcing particles. Either the formation of reinforcement/matrix interfacial layer or the refinement in TiC dendrites/particles microstructures enhanced the microhardness and wear performance of TiC/Inconel 718 composites.Publicationtype: Journal Article27 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Digital photonic production: High power ultrashort lasers, laser additive manufacturing and laser micro/ nano fabrication(Optical Society of America (OSA), 2012-11); ; ; ; The high power optical technologies enter a new era: The age of DIGITAL PHOTONIC PRODUCTION. Very recently new lasers in new time- and wavelength domains with high average powers have been developed for new processes like Laser Additive Manufacturing, Laser Ablation by ultrafast lasers or Laser Polishing.Publicationtype: Conference Paper18 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , High-power ultra-short pulse laser radiation: new sources as key enablers for emerging applications (plenary session keynote)(Laser Inst. of America, 2010-03); ; ; ; Ultrafast laser sources with pulse durations in the sub-picosecond regime enable a precise machining of various materials. Pulse durations shorter than the electron phonon-coupling time lead to a low thermal load or even non-thermal ablation processes. Exploiting non-linear absorption processes, the absorption becomes nearly material independent when laser pulses of several microjoule energy and high beam quality are focused on the materials surface. Low pulse energies and intensities well above the vaporization threshold and therefore an eduction of the absorbed energy within the ablation product enables a high-precision cutting, ablation and drilling of, even weakly absorbing materials, multi-component and multi-layer systems. Additional, the focusing of ultrafast laser pulses in the volume of transparent dielectrics allows a localized modification of the bulk material. Specifically, defined refractive index changes in glasses and crystals can be utilized for waveguiding and beam-forming applications. A combined approach of material modification followed by chemical etching provides the possibility to manufacture micro-channels or 3D-micro mechanical parts. The 3D-capability of the in-volume material processing originates from the non-linear absorption of light in the initially transparent material. To achieve high process efficiencies in material processing, laser sources delivering high average power are necessary. High average power is achieved either by high pulse energies and low repetition rates or high pulse repetition rates and moderate pulse energies. The optimum set of parameters is strongly depending on the process, the material and the application. In this paper, we present compact laser sources with a high flexibility in pulse energy and pulse repetition rate and an average power of several hundreds of Watt. Additional, a broad range of applications, from micro- and nanostructuring of various materials to volume processing of dielectrics will be presented.Publicationtype: Conference Paper15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of process gas sort and pressure on laser percussion drilling(Laser Inst. of America, 2008-10); ; ; Providing the technology to achieve an efficiency of 65 % in natural gas-fired combined cycle power plants is the aim of the German Collaborative Research Center 561 "Thermally highly loaded, porous and cooled multi-layer systems for combined-cycle power plants" at RWTH Aachen University, Germany. For this purpose the fluid temperatures in the gas turbine cycle have to be raised considerably. Therefore a more effective cooling of the thermo-mechanically highly-loaded parts has to be realized, which is achieved by a newly developed effusion cooling requiring cooling holes with a diameter of 0.2 mm at an acute inclination angle of up to 30 °. Within this paper the influences of the process gas sort and pressure on the drilling are investigated concerning drilling velocity, hole quality (recast layer thickness and closures within the hole), and hole geometry (diameter and taper). For the experiments the process gases oxygen, argon, nitrogen, and compressed-air are used with the pressure being varied from 5 to 20 bar. At fixed laser parameters the process gas is determined to have a significant influence on the drilling result.Publicationtype: Conference Paper12