Steel Micro Research Articles

Control of the Nano-Particle Weight Ratio in Stainless Steel Micro and Nano Powders by Radio Frequency Plasma Treatment

This study describes how to make stainless steel hybrid micro-nano-powders (a mixture of micro-powder and nano-powder) using an in situ one-step process via radio frequency (RF) thermal plasma treatment. Nano-particles attached to micro-powders were successfully prepared by RF thermal plasma treatment of stainless steel powder with an average size of 35 μm. The ratio of nano-powders is estimated with a two-dimensional fluid simulation that calculates the temperature profile influencing the rate of surface evaporation. The simulation is conducted to determine the variation of the input power and the distance from the plasma torch to the feeding nozzle. It was demonstrated experimentally that the nano-powder ratio in the micro-nano-powder mixture can be controlled by adjusting the feeding rate, plasma power, feeding position and quenching effect during plasma treatment. The ratio of nano-particles in the micro-nano-powder mixture was controlled in a range from 0.1 (wt. %) to 30.7 (wt. %).

Micro-Shock Tube 유동에 대한 실험적 연구

The flow characteristics in micro shock tube are investigated experimentally. Studies were carried out using a stainless steel micro shock tube. Shock and expansion wave was measured using 8 pressure sensors. The initial pressure ratio was varied from 4.3 to 30.5, and the diameter of tube was also changed from 3mm to 6mm. Diaphragm conditions were varied using two types of diaphragms. The results obtained show that the shock strength in the tube becomes stronger for an increase in the initial pressure ratio and diameter of tube. For the thinner diaphragm, the highest shock strength was found among varied diaphragm condition. Shock attenuation was highly influenced by the diameter of tube.

Sintering behavior of 316L stainless steel micro–nanopowder compact fabricated by powder injection molding

The densification and grain growth behavior of powder injection molded 316L stainless steel micro–nanopowder were investigated in terms of microstructural development. The sintered density of the micro–nanopowder sample increased remarkably in the temperature range of 1000 to 1100°C due to the sintering effect of nanopowders which increased the number of grain boundaries acting as high material transport path. A near full density of 98% TD was obtained after sintering at 1100°C for 5h with the average grain size less than 10μm, indicating that there was no drastic grain growth. The presence of nanopowders in micro–nanopowder played decisive role in the entire sintering process by enhancing densification but suppressing grain growth. These effects open up the possibility of using micro–nanopowder feedstock to control the sintering behavior of powder injection molding products with full density and fine microstructure.

COMPRESSIVE MECHANICAL BEHAVIORS OF HYBRID COMPOSITE MATERIALS BASED ON MICRO LATTICE STRUCTURE AND RUBBERLIKE MATERIALS

ABSTRACT This article investigates compressive and energy absorption characteristics for composites obtained by filling stainless steel micro lattice materials, manufactured via the selective laser melting method, with three different rubbers, including room temperature vulcanization silicone, natural rubber, and neoprene rubber. At the stage of building the composites with natural and neoprene rubbers, an experimental setup was designed for these two rubbers to be infiltrated into lattice spaces under vulcanization temperatures and high pressures. The results showed that the composites with silicone and neoprene matrix had a quite similar response as well as a seriously enhanced energy absorbing capacity and plateau stresses, in comparison with the corresponding lattice structures, for especially small sized lattice components. Also, the compression tests of the composite with natural rubber matrix clearly show that there should be no large differences between the individual mechanical properties of each component in the composite, and, in this way, the contribution of each component on the mechanical behavior of composite should be guaranteed to provide the satisfying performance.

Parametric Scale-Up Cost Factors for Conventional and Micro-Scale Tools

This article estimates cost scale-up factors for micro-scale tools, including high speed steel micro tools, micro thread hand taps, and various types of mesh and wires. Many of these tools initially have a positive scale-up factor where the material costs directly correlate with the cost of the tool; they then transition to a negative scale-up factor at the micro-scale where manufacturing is more difficult and becomes the determining factor for the prices of the products. This article describes the transition from positive to negative scale-up factors, which generally has not been previously reported in the literature. In the future, the negative scale-up factor region of cost estimation could become more important because products, such as electronic hardware, will continue to become smaller in size.

Laser additive manufacturing of stainless steel micro fuel cells

This paper introduces laser additive manufacturing as a new method for the fabrication of micro fuel cells: The method opens up the capability of ultrafast prototyping, as the whole device can be produced at once, starting from a digital 3D model. In fact, many different devices can be produced at once, which is useful for the comparison of competing designs. The micro fuel cells are made of stainless steel, so they are very robust, thermally and chemically inert and long-lasting. This enables the researcher to perform a large number of experiments on the same cell without physical or chemical degradation. To demonstrate the validity of our method, we have produced three versions of a micro fuel cell with square pillar flowfield. All three have produced high current and power density, with maximum values of 1.2 A cm−2 for the current and 238 mW cm−2 for power.

A multi-probe micro-fabrication apparatus based on the friction-induced fabrication method

A novel multi-probe micro-fabrication apparatus was developed based on the friction-induced fabrication method. The main parts of the apparatus include actuating device, loading system, and control system. With a motorized XY linear stage, the maximum fabrication area of 50 mm × 50 mm can be achieved, and the maximum sliding speed of probes can be as high as 10 mm/s. Through locating steel micro balls into indents array, the preparation of multi-probe array can be realized by a simple and low-cost way. The cantilever was designed as a structure of deformable parallelogram with two beams, by which the fabrication force can be precisely controlled. Combining the friction-induced scanning with selective etching in KOH solution, various micro-patterns were fabricated on Si(100) surface without any masks or exposure. As a low-cost and high efficiency fabrication device, the multi-probe micro-fabrication apparatus may encourage the development of friction-induced fabrication method and shed new light on the texture engineering.

Heat transfer correlation for flow boiling in small to micro tubes

There is a large discrepancy in the open literature about the comparative performance of the existing macro and microscale heat transfer models and correlations when applied to small/micro flow boiling systems. This paper presents a detailed comparison of the flow boiling heat transfer coefficient for R134a in stainless steel micro tubes with 21 macro and microscale correlations and models. The experimental database that was used in the comparison includes the data for 1.1 and 0.52mm diameter tubes, mass flux range of 100–500kg/m2s and system pressure range 6–10bar obtained in the course of this study. The effect of the evaporator heated length on the comparative performance of the correlations and models was investigated using three different lengths of the 1.1mm diameter tube (L=150, 300 and 450mm). This comparative study demonstrated that none of the assessed models and correlations could predict the experimental data with a reasonable accuracy. Also, the predictability of most correlations becomes worse as the heated length increases. This may contribute in explaining the discrepancy in the comparative performance of the correlations from one study to another. A new correlation is proposed in the present study based on the superposition model of Chen. The database used in developing the correlation consists of 5152 data points including the current experimental data and data obtained previously with the same test rig, fluid and methodology for tubes of diameter 4.26, 2.88, 2.01mm. The new correlation predicted 92% of the data within the ±30% error bands with a MAE value of 14.3%.

Using micro deep drawing with ironing stages to form stainless steel 304 micro cups

The needs of stainless steel 304 micro cups have been increasing tremendously due to the trend of miniaturization in medical and electronic devices, etc. For application purpose, it is highly desired to have stainless steel micro cups with high CH/OD (cup height/outer diameter) ratios. Due to the constraints of the limit draw ratio (LDR) of stainless steel 304 sheets in micro deep drawing, forming a micro cup with high CH/OD ratio at room temperature cannot be achieved by using a single stage deep drawing die. A process consisting of one micro deep drawing and two ironing stages was proposed for achieving this goal; three micro dies were designed, fabricated and used for experimental validation. A series of experiments were conducted by using the stainless steel 304 sheets of 200μm thickness annealed at four different temperatures to understand the influence of size effects on this process for generating knowledge, know-how and technologies to form high quality stainless steel micro cups with large CH/OD ratio. No lubricant was used in this study. It was proven that the proposed process is a robust process as long as the sheets are annealed at the temperature no less than 900°C for more than 3min.

Experimental Investigation of Ultra-high Performance Fiber Reinforced Concrete Slabs Subjected to Deformable Projectile Impact

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is currently one of the biggest challenging issues in modern concrete technology. The UHPFRC represents a concrete with improved durability and strength, which is significantly higher than in conventional normal strength concrete. This may result in reduced cross-sections and as a consequence smaller dead-load of the structure. The uniaxial compressive cylinder strength of UHPFRC used in this study exceeded 150MPa and the uniaxial direct tensile strength exceeded 10MPa. Several UHPFRC mixtures with different content of fibers were subjected to deformable projectile impact. The ogive-nose projectile weighed 8.04 grams and its average velocity was determined to be 710 m/s. It was shown that plain UHPC specimen failed in the brittle manner which caused that the slab split into several pieces. Further, it was demonstrated that addition of steel micro fibers enhanced the resistance to deformable projectile impact and it was specified that specimens containing 2% of fibers by volume have optimal resistance against impact loading. In addition, response of slabs made of conventional fiber reinforced concrete (FRC) and normal strength concrete (NSC) was studied for comparison. The magnitude of the damage was assessed based on the penetration depth, crater diameter and mass loss. Experimental results clearly showed that implementation of high strength steel micro fibers significantly increased the resistance to projectile impact. It was stated, that UHPFRC has much better resistance to projectile impact in comparison to conventional FRC.

Simulation and Experimental Study on Size Effect in Steel Micro Milling Machining Process

Size effect is a critical factor that needs to be considered when conducting micro mechanical machining processes. In this paper, a cutting process simulation technology is used to simulate a single tooth’s engagement with workpiece from the entry point to the exit point in a slot milling operation. The obtained specific cutting forces from simulation are employed to analyze the size effect and the minimum chip thickness with variable radii of tool edges. Micro machining experiments with different machining conditions are implemented by use of a high speed and high precision machining spindle to investigate the size effect on machined surface integrity and burr width. The optimal cutting parameters have been analyzed based on the simulation and cutting test results.

Plastic Micro Features Produced by Microwelding Machine

The method of using microwelding machine to fabricate micro features on a stainless steel micro mould has been studied. The micro features obtained from molding using an ultrasonic microwelding machine have shown distinctive characteristics. The microflow behavior of polymer melt during the microwelding process is also studied. The micro molds of 0.2mm thick and through holes of 0.05mm and 0.2mm in diameters were used. Results show micro features can be produced using the microwelding machine with molding speed comparable to that of micro injection molding.

Verification of a Finite Element Simulation of the Progressive Collapse of Micro Lattice Structures

Stainless steel micro lattice structures, manufactured by selective laser melting, have the potential to be used as core materials in twin skinned structures. The configuration considered here is body centred cubic. One of the major structural performance requirements for such twin skinned structures is foreign object impact. The paper describes the series of steps taken to simulate (using DYNA) and validate the low velocity foreign object impact behaviour of twin skinned panels with micro lattice cores. This includes the validation of a three beam model for each micro strut, the modelling of node behaviour, and the modelling and validation of compressed micro lattice blocks, and of full foreign object impact panel behaviour.

Preparation and characterization of micro components fabricated by micro powder injection molding

Abstract Given the dimension of the micro component to be replicated, it is crucial to study sintering for dimensional and property control in micro powder injection molding. In the paper, 316 L stainless steel micro components with two different microsize structure dimensions, ϕ100 μm × height 200 μm and ϕ60 μm × height 191 μm, are fabricated from in-house feedstock. Shrinkage, microstructure, microindentation hardness and sintering trajectory are investigated for the micro components. The linear shrinkage rate of the micro component reaches the maximum at 1180 °C, after which it begins to decline. Porosity (volume fraction of pores) decrease, pore migration and breakaway, grain growth and the formation of a dense layer are observed for the microsize structures. The microindentation hardness of the dense layer in the rim of the microsize structures is lower than the microindentation hardness of the substructure. It is found that if the relative density is below 0.98, densification is promoted when the structure size reduces from the substructure in the millimeter regime to the microsize structures of ϕ60 μm. This is attributed to the oxides on the debound micro components and internal gas pressure produced by hydrogen sintering.

Microstructure evolution of 316L stainless steel micro components prepared by micro powder injection molding

Fabrication of micro components comprising of functional units of different dimensional order, ϕ100 μm, ϕ80 μm and ϕ60 μm, by micro powder injection molding is described in the paper. The microstructure is characterized for various microsize structures and substructures under different sintering conditions. The micro components are successfully molded, debound and sintered based on an in-house feedstock. Although sintered as an integral component, the microsize structure is at final stage sintering whereas the substructure is at intermediate stage sintering within the temperatures studied. The smallest microsize structures, ϕ60 μm, have the highest relative density. Higher surface area/volume ratio of the microsize structures is attributed to the advanced sintering. XPS results show that oxides on the debound micro components and consequent reduction products during hydrogen sintering attribute to the formation and progression of the observed dense layers.

Test rig for micro gear and experimental analysis on the meshing condition and failure characteristics of steel micro involute gear and metallic glass one

A test rig to evaluate the performance of a micro involute gear with a diameter below 1 mm has been developed. Shaft position and shaft center distance of gears have great influence on the gear performance and therefore they must be adjusted precisely. In this research, the measurement and adjustment method of gear assembly condition and an in-situ observation system of gear condition are proposed, that are appropriately designed for micro gears. The meshing condition of micro involute gears is investigated experimentally. Based on the observation of sliding marks on the tooth flank, it is clarified that the meshing condition of a micro involute gear follows the meshing theory of an involute gear. Failure modes of SK4 micro gears and metallic glass micro gears are investigated. The experimental results indicated that SK4 micro gears suffer severe wear under unlubricated conditions that generate powderlike wear particles. On the other hand, flakelike wear particles appear in the metallic glass micro gear.

H2S corrosion inhibition of an ultra high strength pipeline by carboxyethyl-imidazoline

The H2S corrosion inhibition of ultra high strength steel with carboxyethyl-imidazoline has been evaluated with electrochemical techniques. Tested material included a water quenched Fe–C–Mn steel micro alloyed with Si, Nb, Cr, and Ti, equivalent to an API X-120 pipeline steel, whereas electrochemical techniques included polarization curves, linear polarization resistance, electrochemical impedance spectroscopy, and electrochemical noise measurements. Tested solutions included H2S-containing 3% NaCl with and without 10 vol% of diesel and different inhibitor concentrations (0, 5, 10, 25, 50, and 100 ppm) at 50 °C. Different techniques have shown that the optimum carboxyethyl-imidazoline efficiency was obtained with 50 ppm, but the efficiency decreases as time elapsed. Corrosion rates obtained with diesel were lower than those obtained without diesel.

Fabrication of 316-L stainless steel micro components using encapsulating soft mould and isopressing technique

This paper presents in detail a new method to fabricate free standing 316-L stainless steel micro components using high solid loading stainless steel semi solid paste encapsulated into soft mould (PDMS) and pressed using hydrostatic pressure. The process is divided into five parts: (i) production of SU-8 master moulds and their negative replicas from soft moulds, (ii) preparation of stainless steel semi solid paste with high solid loading and filling the soft mould insert, (iii) the soft mould is sealed well and put under hydrostatic pressure, (iv) after the pressure is released the soft mould seal is removed and the paste is left to dry, (v) the green parts are obtained, de-bound, and sintered in vacuum at 1350 °C. The effect of the applied hydrostatic pressure on both the green and sintered densities as well as the linear shrinkage of the micro components was investigated in detail and compared with the pressure-less filling method. It is found that both the green and sintered densities increase while the linear shrinkage decreases with the increase of applied hydrostatic pressure. The maximum sintered density and its corresponding linear shrinkage were found to be 98.6% and 13%, respectively.

The characteristics of cutting forces in the micro-milling of AISI D2 steel

The interaction effect of parameters to surface topography and cutting forces is investigated, and the magnitudes of these parameters are determined in the micro-milling of AISI D2 steel. The results show that the feed per tooth has a prominent impact on the surface topography. Due to the low feed per tooth to cutting edge radius ratio, a high surface roughness and a high amount of burrs are obtained in micro-milling. In micro cutting, the cutting forces present are small; in addition, the radial thrust cutting forces are greater than the principal cutting forces. This research proves that the micro-milling process can be applied to the manufacturing of AISI D2 steel micro parts and presents experimental evidence and possible solutions to the cutting parameters.

Development of WC-Co/SUS304 Functionally Graded Materials by Using Three Dimensional Micro Welding

Three dimensional micro welding (3DMW) of a novel freeform fabrication process for metal or alloy components has been developed in our investigation group. A tungsten inert gas (TIG) welding machine is controlled by utilizing CAD/CAM processes. Various types of metal or alloy wires are fed automatically under a micro-arc torch to form tiny metallic beads. These micrometer order beads are joined continuously to build three dimensional structures. Near-net-shape components of metal or alloy compounds with high melting points can be fabricated automatically with minimized energy and resources. In this study, tungsten carbide-cobalt (WC-Co) and stainless steel (SUS304) micro beads of 1.0 mm in diameter were stacked alternately to fabricate cutting tools with graded structures by using the 3DMW. The microstructure and hardness were observed by scanning electron microscope (SEM), energy dispersive spectra (EDS) and Vickers hardness tester. The maximum hardness of micro bead was approximately 1300 HV and no crack or pore existed in the formed objects.