Controlled Post-treatment of Thick CVD-Diamond Coatings by High-Density Plasma Oxidation

CVD-diamond coatings were posttreated by plasma oxidation to recycle an original WC (Co) mother tool substrate for recoating and reuse. A developed RF/DC plasma oxidation system was stated together with a hollow cathode device to intensify the oxygen ion and electron densities and with a quantitative plasma diagnosis equipment. Plasma oxidation ashing conditions were optimized by this quantitative diagnosis toward the perfect ashing of diamond films with less residuals and less tool edge damage. Geometric effect of tool teeth structure on this ashing process was discussed by in situ monitoring of plasmas. Engineering solution of this ashing process was proposed for industrial applications

Low Temperature Plasma Nitriding of Austenitic Stainless Steels

A low temperature plasma nitriding process has become one of the most promising methods to make solid-solution hardening by the nitrogen super-saturation, being free from toxicity and energy consumption. High-density radio-frequency and direct current (RF/DC) plasma nitriding process was applied to synthesize the nitrided AISI304 microstructure and to describe the essential mechanism of inner nitriding in this low temperature nitriding (LTN) process. In case of the nitrided AISI304 at 673 K for 14.4 ks, the nitrided layer thickness became 66.5 μm with the surface hardness of 1550 HV and the surface nitrogen content of 9 mass%. This inner nitriding process was governed by the synergetic interrelation among the nitrogen super-saturation, the lattice expansion, the phase transformation, the plastic straining, the microstructure refinement, and the acceleration of nitrogen diffusion. When this interrelation is sustained during the nitriding process, the original austenitic microstructure is homogeneously nitrided to have fine-grained microstructure with the average size of 0.1 μm. Once this interrelation does not work anymore, the homogeneous microstructure changed itself to the heterogeneous one. The plastic straining took place in the selected coarse grains so that the parts of them were only refined. This plastic localization accompanied with the localized phase transformation

Pico- and Femtosecond Laser Micromachining for Surface Texturing

The pico- and femtosecond laser micromachining has grown up as a reliable tool for precise manufacturing and electronic industries to make fine drilling and machining into hard metals and ceramics as well as soft plastic and to form various nano- and microtextures for improvement of surface functions and properties in products. The ultrashort-pulse laser machining systems were developed to describe the fine microdrilling and microtexturing behavior for various materials. Accuracy in circularity and drilled depth were evaluated to discuss the effect of substrate materials on the laser microdrilling. Accuracy in unit geometry and alignment was also discussed for applications. A carbon base mold substrate was micromachined to transcribe its microtextures to transparent plastics and oxide glasses. Three practical examples were introduced to demonstrate the effectiveness of nano-/microtexturing on the improvement of microjoinability, the reduction in friction and wear of mechanical parts and tools, and the surface property control. The fast-rate laser machinability, the spatial resolution in laser microtexturing as well as the laser micromanufacturing capacity were discussed to aim at the future innovations in manufacturing toward the sustainable society

Micro-/Nano-Structuring in Stainless Steels by Metal Forming and Materials Processing

Austenitic stainless steel type AISI304 sheets and plates as well as fine-grained type AISI316 (FGSS316) substrates and wires were employed as a work material in the intense rolling, the piercing and the plasma nitriding. AISI304 sheet after intense rolling had textured microstructure in the rolling direction. Crystallographic state changed itself to have distorted polycrystalline state along the shearing plane by piercing, with the strain induced phase transformation. FGSS316 substrates were plasma nitrided at 623 K for 14.4 ks to have two-phase fine nanostructure with the average grain size of 100 nm as a surface layer with the thickness of 30 μm. FGSS316 wires were also plasma nitrided at the same conditions to form the nitrided surface down to the depth of 30 μm. This nitrided wire was further uniaxially loaded in tensile to attain more homogeneously nitrided surface nano-structure and to form the austenitic and martensitic fiber structure aligned in the tensile direction. Each crystallographic structure intrinsic to metals and metallic alloys was tailored to have preferable micro−/nano-structured cells by metal forming and nitrogen supersaturation. The crystallographic change by metal forming in a priori and posterior to nitriding was discussed to find out a new way for materials design

Integrated Manufacturing of Fine-Grained Stainless Steels for Industries and Medicals

Austenitic stainless steels have been widely utilized in industries, infrastructures, housing structures, kitchen components, and medical tools. Higher hardness and strength as well as more improvement of wear and corrosion toughness are often required in the industrial and medical applications. Fine-grained stainless steel (FGSS) provides a solution to increase the strength without loss of ductility and toughness. Deeper research and development in manufacturing of FGSS is required to make full use of its properties toward its applications in industries and medicals. First, its mechanical properties and microstructure is introduced as a basic knowledge of FGSS with comparison to the normal stainless steels. Mechanical and laser machinability of FGSS is stated and discussed to finish the products in seconds. Its performance in metal forming and diffusion bonding is explained to explore its applications in third. Its surface treatment and tooling is discussed to describe the grain-size effect on the low temperature plasma nitriding and to demonstrate its effectiveness in die-making in forth. Finally, every aspect in manufacturing of FGSS sheets and solids is summarized as a conclusion

Plasma Nitriding-Assisted 3D Printing for Die Technology in Digital Micro-Manufacturing

A plasma nitriding-assisted 3D printing method was developed to build up the micro-punch and micro-die systems. Two dimensional punch head and core-die cavity geometries were ink-jet printed or screen-printed onto the AISI316 and SKD11 tool substrate surfaces in following their two-dimensional computer-aided design (CAD) data. The low-temperature plasma nitriding process was utilized to make nitrogen supersaturation only into the unprinted substrates. The sand-blasting and chemical etching were utilized to mechanically or chemically remove the printed parts from punch and die substrate. As sand-blasted and chemically etched AISI316 and SKD11 punches and core-dies were simply finished and used as a die set for micro-embossing, micro-piercing and micro-punching processes. In particular, a micro-pump was selected as a miniature mechanical element. Its 3D CAD geometry was sliced to 2D CAD data for each functional AISI304 stainless steel sheet. A pair of punch and die for each 2D CAD geometry for constituent sheet was prepared by the plasma nitriding-assisted 3D printing. Each sheet was punched out by using this set of punch and die to functionalize each sheet unit in correspondence to the sliced CAD data. These constituent sheets were assembled and joined to a structural unit of micro-pump

Heat Transportation by Acicular Micro-Textured Device with Semi-Regular Alignment

Heat transportation device was developed to improve the cooling capacity through the heat convection process and to make low-temperature radiation from the heat source to the objective body in vacuum. This device consisted of the metallic substrate and the acicular micro−/nano-textures in semi-regular alignment. The micro-cone unit cell size and pitch in these textures was controllable by tuning the total current and the current density in the electrochemical processing. Four devices with various unit cell sizes and pitches were prepared for geometric characterization by SEM (Scanning Electron Miscopy) and for spectroscopic analyses on the IR-emittance by FT-IR (Fourier Transform-InfraRed) spectroscopy. Heat radiation experiment was performed to describe the heat transportation in vacuum from the heat source at 323 K to the objective plate. The texture size effect on the low-temperature heat radiation was investigated to build up a physical model for this heat radiation device. Heat convection experiment was also performed to describe the cooling capacity of device under the forced air flow. The unit cell height effect on the cooling behavior was discussed to deduce the physical model for this heat convection device. These models were considered to be used in the computational fluid mechanics simulations

Fabrication of SUS304 Regularly Cell-Structured Material and Their Mechanical Properties

The quasi-static flexural and in-plane compressive properties of SUS304 stainless steel with circular close-packed cells are studied. Microstainless steel tubes coated with Ni 3 P were selected for constructing hexagonal close-packed arrays, which are subsequently joined together to form a cellular structure. The fabrication technique developed, involves the diffusion bonding of stacked metal tubes under the compressive stress state during heat treatment. SUS304 cell-structured materials can achieve the high specific flexural stiffness and specific flexural yield strength nearly equal to those for the dense materials. In-plane compressive properties as well as deformation behavior are also observed and discussed in this paper

Laser Treatment CVD Diamond Coated Punch for Ultra-Fine Piercing of Metallic Sheets

CVD-diamond coated special tools have been widely utilized to prolong their tool life in practical production lines. WC (Co) punch for fine piercing of metallic sheets required for high wear-toughness to be free from chipping and damages and for high product quality to punch out the holes with sufficient dimensional accuracy. The laser trimming process was developed to reduce the surface roughness of diamond coating down to submicron level and to adjust its diamond layer dimensions with a sharp punch edge for accurate piercing. The pulsed laser irradiation was employed to demonstrate that micro-groove was accurately formed into the diamond coating. Less deterioration in the worked diamond film by this laser treatment was proved by the Raman spectroscopy. The femtosecond laser trimming was proposed to sharpen the punch edge down to 2 μm and to form the nano-textured punch side surfaces with the LIPSS (Laser Induced Periodic Surface Structuring)-period of 300 nm. Fine piercing experiments were performed to demonstrate that punch life was significantly extended to continuous punching in more than 10,000 shots and that mirror-shining hole surfaces were attained in every shot by regularly coining the nanotextures. The sharp punch edge with homogeneous edge profile was responsible for reduction of the induced damages into work sheet by piercing. The punch life was extended by the ejection mechanism of debris particles through the nanotextures on the punch side surface. The present laser treatment was useful in trimming and nanostructuring the complex-shaped punch edge for industrial application

Nitrogen Supersaturation of AISI316 Base Stainless Steels at 673 K and 623 K for Hardening and Microstructure Control

The high-density plasma nitriding at 673 K and 623 K was employed to make 10% of nitrogen supersaturation on AISI316 base austenitic stainless steels. The processing parameters and nitrogen-hydrogen gas flow ratio were optimized to increase the yield of N2+ ion and NH-radical for efficient nitriding. The nitrided AISI316 specimens were prepared for multidimensional analysis to describe the fundamental features of low-temperature plasma nitriding. First, macroscopic evaluation revealed that nitrogen supersaturation induced the γ-lattice expansion and the higher nitrogen content than 4% of mass in depth. The mesoscopic analysis describes the holding temperature and initial grain-size effects on the microstructure changes. Plastic straining, grain-size refinement, and nitrogen zone-boundary diffusion processes advance with nitrogen supersaturation to drive the inner nitriding behavior. The microscopic analysis explains the microstructure refinement, the two-phase structuring, and the microstructure modification. Through this multi-dimensional analysis, the essential characteristics of the low-temperature plasma nitriding of 316 austenitic stainless steels were precisely understood to extend the engineering treatise on the bulk nitrogen stainless steels for surface modification and treatment of stainless steels by nitriding. This plasma nitriding was applied to strengthen and harden the AISI316 wire surfaces toward its application on surgery wires