• Journal of the Korean institute of surface engineering
• /
• v.47 no.1
• /
• pp.13-19
• /
• 2014

The various surface treated conditions of Fe-3.0%Ni-0.7%Cr-1.4%Mn-X steel such as as-received, ion nitriding, DLC coated, DLC coated after nitriding for 3 hrs and 6 hrs were investigated to evaluate the beneficial effect for plastic mold steel. Micro Vickers hardness tester was used to estimate nitriding depth from the hardness profile and to measure hardness on the surface. Elastic modulus and residual stress were measured by a nanoindentator. Scratch test and SP (small ball punch test) were utilized to assess the adhesive strength of DLC coating. The depth of nitriding layer was measured as $50{\mu}m$ for the condition of 3 hrs nitriding and $90{\mu}m$ for that of 6 hrs nitriding. Hardness, elastic modulus, residual stress of DLC coating were 20.37 GPa, 162.78 GPa and -1456 MPa respectively. Residual stress on the surface of DLC coating after nitriding could increase to -3914 MPa by introducing nitriding before DLC coating. During the 'Ball-On-Disc' test ${\gamma}^{\prime}$ particles pulled out from the surface of nitrized layer tend to enhance abrasive wear mode since the fraction of ${\gamma}^{\prime}$ (Fe4N) in ion-nitrized layer is known to increases with nitriding time. Thus the specific wear rate of the nitriding layer increased. Comparing with nitriding the specific wear rate in work piece disc as well as ball decreased prominently in DLC coating due to the remarkable reduction in friction coefficient.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.12 s.177
• /
• pp.124-130
• /
• 2005

The research on surface modification technology has been advanced to improve the properties of engineering materials. ion implantation is a novel surface modification technology to enhance the mechanical, chemical and electrical properties of substrate's surface using accelerated ions. In this research, nitrogen ions were implanted into aluminum substrates which would be used for mold of rubber materials. The composition of nitrogen ion implanted aluminum alloy and nitrogen ion distribution profile were analyzed by Auger Electron Spectroscopy (AES). To analyze the modified surface, properties such as hardness, friction coefficient, wear resistance, contact angle, and surface roughness were measured. Hardness of ion implanted specimens was higher than that of untreated specimens. Friction coefficient was reduced, and wear resistance was improved. From the experimental results, it can be expected that ion implantation of nitrogen enhances the surface properties of aluminum mold.

• Journal of the Korean Society for Precision Engineering
• /
• v.1 no.2
• /
• pp.24-32
• /
• 1984

The object of the study is to discuss the effect of magic ink as a surface active substance on the mechanism of chip formation in oblique cutting. The Rehbinder effect has been known as a phenomenon that the mechanical strength reduces when the metal is coated with some surface active substances. In order to interpret these surface effects defined by Rehbinder, the influence on the shear strength of shear plane by coating surface active substances, cutting force by the depth of cut, surface roughness and hardness ratio were observed. The results are as follows: 1. By coating the magic ink on free surface of the forming chip, the effective shear angle increases, and the cuttinbg force and the deformed chip thickness decreases. 2. With the large inclination angle the effective shear angle increases, and the specific cutting force and the friction angle decrease. 3. Cutting of the coated surface improves the surface roughness and the hardness ratio drops, which means another Rehbinder effect.

• Journal of the Korean institute of surface engineering
• /
• v.42 no.5
• /
• pp.246-249
• /
• 2009

Cu-Ti alloys with titanium in the range of 0.5-6.0 wt% were developed to evaluate the effect of the titanium content and heat treatment on microstructure, hardness, and electrical conductivity. The hardness of the Ti-added copper alloys generally increased with the increase in titanium content and hardening was effective up to the 2.5 wt%-Ti addition. Microstructural examination showed that the second phase of $Cu_4Ti$ started to precipitate out from the 3.0 wt% Ti-addition, and the precipitate size and volume fraction increased with further Ti addition. Aging of the present Cu-Ti alloys at $450^{\circ}C$ for 1 h increased the hardness; however, the further aging up to 10 h did not much change the hardness. In the present study, it was inferred that in optimal Ti addition and aging condition Cu-Ti alloy could have the hardness and electrical conductivity values which are comparable to those of commercial Cu-Be alloy.

• Journal of the Korean institute of surface engineering
• /
• v.38 no.2
• /
• pp.79-82
• /
• 2005

This study investigated the effect of nitriding on the hardness and adhesion properties of $TiB_2$ coatings. Inductively coupled plasma (ICP) was used for both nitriding and deposition. By applying ICP, H13 steel was nitrided at a high rate of $50\;{\mu}m/hr$. After nitriding, a Fe4N compound layer or a diffusion layer was formed according to the hydrogen/nitrogen ratio. Both layers could improve the load-bearing capacity of the substrate by increasing the substrate hardness. The adhesion of the $TiB_2$ coatings increased to $\~30N$ after nitriding, but the hardness of the coating was lowered to 20-30 GPa. However, the adhesion of the $TiB_2$ coatings with a high hardness (>60 GPa) could not be improved substantially by nitriding due to the large difference in hardness between the coating and the substrate. The grain size of the $TiB_2$ coating was larger on the nitrided substrates, resulting in a decrease in the hardness of the coating.

• Journal of the Korean institute of surface engineering
• /
• v.16 no.1
• /
• pp.3-9
• /
• 1983

The change of the hardness and yield strength depending upon the electrolysis conditions was investigated for Watts and bright nickel electrodeposits. The hardness of Watts nickel electrodeposits decreased with increasing current density in the range of 1-15A/Am2, while it increased with increasing bath temperature. The hardness of bright nickel deposits increased noticebly in comparison with that of Watts nickel electro-deposits. The hardness and the yield strength of the bright nickel electrodeposits increased considerably with decreasing current density and the highest value was obtained at the lowest current density (1A/dm2), while they decreased noticebly at the bath temperature of 80$^{\circ}C$ in comparison with that of 40-60$^{\circ}C$. The change of the hardness and the yield strength of bright nickel electrodeposits depending upon the electrolysis conditions could be mainly attributed to the variation of organic additives codeposited in the electrodeposits. The recrystallizatioin temperature(50% softening temperature) of the Wattss and the bright nickel electro-deposits was 520-280$^{\circ}C$ and 350-410$^{\circ}C$ respectively and then the recystallization temperature of bright nickel deposits was lower than that of the Watts nickel electrodeposits.

• Journal of the Korean institute of surface engineering
• /
• v.46 no.1
• /
• pp.48-53
• /
• 2013

In the present work, it was investigated a behavior of hydrogen embrittlement at the subsurface zones of 590 DP steels by using the micro-Vickers hardness test. The micro-Vickers hardnessess of DP steels were measured to evaluate the degree of embrittlement as the effective hardening depths of subsurface zones with hydrogen charging conditions. The results showed that the distributions of micro-Vickers hardness in width varied from maximum hardness 239.5 Hv to minimum hardness 174 Hv, while the depth of effective hardening layer at the subsurface zones of DP steels was from $320{\mu}m$ to $460{\mu}m$ with hydrogen charging conditions, respectively. It was proposed that the distribution of microhardness be used as the evaluation index of the degree of embrittlement. But the variations of martensite volume fractions were not affected along depth of hardening at the same changing time, hydrogen charging times were appeared as an effective factor of the degree of embrittlement. Therefore, the micro-Vickers hardness test is an attractive tool for evaluation of hydrogen embrittlement at the subsurface zones of these DP steels.

• Transactions of Materials Processing
• /
• v.32 no.4
• /
• pp.180-190
• /
• 2023

This study deals with residual stress prediction and hardness evaluation within cross ball grooved inner race fabricated by cold upsetting process consisted of upsetting and ejection steps. A raw workpiece material of AISI 5120H (SCr420H) is first spheroidized and annealed, then phosphophyllite coated to form solid lubricant layer on its outer surface. To investigate influences of the heat treatment, uni-axial compression tests and Vickers micro-hardness measurements are conducted. Three-dimensional elasto-plastic FE simulations on the upsetting step and the ejection one are performed to visualize the residual stress and the ductile (plastic deformation) damage. External feature of the fabricated inner race is fully captured by using an optical 3D scanner, and the micro-hardness is measured on internal cross-sections. Consequently, the dimensional compatibility between the simulated inner race and the fabricated one is ensured with a difference of under 0.243mm that satisfied permissible error range of ±0.50mm on the grooved surface, and the predicted residual stress is verified to have similar distribution tendency with the measured Vickers micro-hardness.

• International Journal of Precision Engineering and Manufacturing
• /
• v.7 no.1
• /
• pp.57-61
• /
• 2006

The research on surface modification technology has been advanced to improve the properties of engineering materials. Ion implantation is a novel surface modification technology that enhances the mechanical, chemical and electrical properties of substrate's surface using accelerated ions. In this research, nitrogen ions were implanted into AC7A aluminum substrates which would be used as molds for rubber molding. The composition of nitrogenion implanted aluminum and distribution of nitrogen ions were analyzed by Auger Electron Spectroscopy (AES). To analyze the modified surface, properties such as hardness, friction coefficient, wear resistance, contact angle, and surface roughness were measured. Hardness of ion implanted specimen was higher than that of untreated specimen. Friction coefficient was reduced, and wear resistance was improved. From the experimental results, it can be expected that implantation of nitrogen ions enhances the mechanical properties of aluminum mold.

• Food Science and Preservation
• /
• v.4 no.3
• /
• pp.337-341
• /
• 1997

Texture is an important quality factor of processed chestnut products, which changes depending on the conditions of boiling process. The conventional boiling process consists of three stage(1st : 70 minutes at 60$^{\circ}C$; 2nd : 20minutes at 70$^{\circ}C$; 3rd : 80minutes at 98$^{\circ}C$). To improve the conventional boiling process of processed chestnut products, we investigated the changes of texture at different stages of boiling process and undertook the optimization of boiling process by response surface method on heating times of 2nd and 3rd heating, and amount of softening agent. The initial hardness and cohesiveness, the most important textural characteristics of chestnut, were 7.876kg and 0.189, respectively. In the third boiling stage, hardness decreased to 0.313kg and cohesiveness increased to 0.310. Using response surface method the minimum point of hardness and maximum point of cohesiveness was examined and model equations for predicting the changes of hardness and cohesiveness in the optional boiling condition were developed.