Utilisation of silicon rubber to characterise tool surface quality during die compaction

Abstract

A new methodology was developed to observe and measure tool wear and tool surface quality during the die compaction process. The newly developed method is a non-destructive test that relies on silicon rubber to transcribe the inner surface profile of the compaction die. After verification of the method, aluminium and iron alloy powders were compacted to quantify tool wear and tool surface quality with two die materials, tungsten carbide and tool steel. The tool surface quality was quantified by recording surface roughness of the die replicas on a surface profilometer.     

Influence of cooling and reheating on the evolution of copper rich liquid in high residual low carbon steels

Abstract

This study investigates some effects of austenite microstructure on processes leading to copper hot shortness. Low carbon steels containing 0˙55 wt-% copper were subjected to two thermal profiles in an infrared image furnace with attached confocal scanning laser microscope: hold at 1150°C for 60 s; hold at 1150°C for 60 s, quench to 400°C, reheat to 1150°C. Heat treatments were conducted in dried/deoxidised argon to image microstructures. Subsequent samples were oxidised in air. The oxide/metal interface was studied in a scanning electron microscope. Additional confocal scanning laser microscope experiments involved melting copper directly on the steel. After quench/reheat, austenite grain size decreased by a factor of ～1˙7 and grain boundaries were redistributed. Copper evolved during the first heating was no longer found at boundaries. Results from direct copper exposure reveal an apparent effect of boundary character on copper penetration rate. Possible mechanisms by which hot shortness is affected are discussed.     

Influence of atomising gas pressure on 63A solder powder in supersonic atomisation

Abstract

The atomising gas pressure is one of several important process parameters that affect the characteristics of the powder particles. The work analyses qualitatively the influence of the atomising gas pressure on 63A solder alloy fine powders. Also studied was the mechanism of the effect of the atomising pressure on the base of the air dynamics through the atomising 63A solder alloy experiment with different atomising pressures on the supersonic nozzle. The results indicate that 63A solder alloy fine powders may be attained, which can satisfy the SMT application requirement when the atomising gas pressure is at 0.7 MPa.     

Influence of Erroneous Data on the Results of Calculations From Acid–Base Surface Free Energy Theories. III. Solution of a Three-Equation Set in the Case of Homoscedastic Error

The van Oss–Chaudhury–Good theory (vOCGT) was checked for a large artificial set of work of adhesion input data calculated for 15 solids and 300 liquids. Numerical values of LW component and acid (A) and base (B) parameters were assigned to 15 solids. These 15 solids were grouped in 5 sets of 3 solids in each. Also numerical values of LW component and A and B parameters were assigned to 300 liquids (three sets of 100 liquids in each). Data for these solids and liquids were especially selected to represent real types of materials encountered in practice. For all 15 solids and 300 liquids the work of adhesion values were calculated and these values were assumed to be error-free. Next, new values of the work of adhesion were obtained by adding a random homoscedastic error (A vector of random variables is homoscedastic if it has the same finite variance.) of the normal distribution (Also called the Gaussian distribution — it is continuous probability distribution defined by two parameters: the mean and variance (standard deviation squared, σ ²).), belonging to 8 distributions of a mean value equal to the error-free work of adhesion value and standard deviations of 0.5, 1, 2, 5, 7, 10, 15 and 20 mJ/m². The LW components and A and B parameters for these solids were back-calculated for each error level. Two different methods for the solution of a 3-equation set were used and they gave practically the same results irrespective of the error level and liquids and solids used. It was found that there existed a linear correlation between the RMSE (root mean square error) of the solution and the standard deviation of the work of adhesion data. This correlation was highly significant (with a correlation coefficient higher than 0.999) and was true separately for LW component, A and B parameters as well as for the total solution vector (i.e., combinedly for the LW component, A and B parameters). The RMSE values of the total solution vector (having as elements values of the LW component, A and B parameters) as well as separately for LW component and A and B parameters were correlated with the condition number of a given 3-equation set. A very good correlation was found only for the total solution, much worse for A or B parameters, and practically there was a lack of correlation for the LW component. Based on the correlation between the RMSE and the standard deviation of the work of adhesion it was possible to determine what should have been the maximal standard deviation of the work of adhesion if the calculated value of a given LW component or A or B parameter did not differ by more than 1 mJ/m² from an error-free (true) value.     

Improvement of Adhesion Between Liquid Crystalline Polyester Films by Plasma Treatment

Surface modification of thermotropic liquid crystalline aromatic polyester (LCP) films was carried out by low-pressure plasma treatment to improve the initial adhesion as well as the long-term adhesion reliability, a measure of durability between the LCP films used as substrates for printed circuit boards. Plasma irradiation was carried out in various plasma gases with different plasma modes such as reactive-ion-etching, and direct-plasma (DP) with pressures ranging from 6.7 Pa to 26.6 Pa. The introduction of polar groups on the film surface such as phenolic hydroxyl groups and carboxyl groups enhanced the initial adhesion by increased chemical interaction. However, if the concentration of polar groups became too high, the longterm adhesion reliability estimated by the pressure cooker test was degraded due to the acceleration of the penetration of water molecules into the interface. A large surface roughness was also effective in preventing the decrease in the long-term adhesion reliability. However, too much increase in surface roughness decreases the long-term adhesion reliability. The DP-treatment in the O₂ atmosphere at a gas pressure of 6.7 Pa was found to be the best plasma condition for both the initial adhesion as well as the long-term adhesion reliability between the LCP films.     

Investigation of the relationship between statistical characteristics of substrate surface roughness and the strength of adhesive joints

The relationship between statistical characteristics of butadiene styrene rubber (BSR) surface roughness and shear strength of adhesive joints has been investigated. The assumption of stationary normal distribution of coordinates of surface points was made to determine the statistical characteristics of surface roughness. The profile length above the selected level l ₁ (u) was introduced as a new surface roughness parameter to characterize adhesive penetration depth. The validity of simulated l ₁ (u) value was verified experimentally. A good correlation between experimental and calculated results was found. A relationship between adhesive penetration depth and the bonding pressure during adhesive joint preparation was also obtained. The dependences among lap shear joint strength, bonding pressure and roughness characteristic l ₁ (u) were determined.     

Characteristics of Acoustic Emission Signal Specific to Isolated Cracks Triggered by Scratch Tests in Stainless Steel Coatings

The tribological process during contact between two surfaces involves mechanical and tribochemical changes as well as material transfer. PVD coatings have a complex structure, and there is a need to characterize the failure of such coatings and this has been carried out by a non-destructive method, namely acoustic emission. In this paper simple scratch tests are described in order to study some characteristics of nitrogen-doped stainless steel coatings on 40CrMo4 construction steel. Scratch tests were performed in order to induce a mechanical failure in the coatings. The aim of this paper is to show that the nucleation of isolated cracks mechanism that leads to failure can be monitored by certain characteristics of the acoustic emission signal.     

Structural stability and non-catalytic nucleation inhibition effect of Si–Zr–B mould coating on undercooled superalloy melt

Abstract

The investment moulding technique was first adopted to prepare a SiO₂–ZrO₂–B₂O₃ (Si–Zr–B) substrate layer on the inner surface of the mould, by employing SiO₂ glass dust and ZrO₂ powder, SiO₂–ZrO₂ sol, and analytical grade H₃BO₃ as refractory material, binder, and softening agent, respectively. Then using sol–gel processing, seven layers of Si–Zr–B film of the same formula as the aforementioned Si–Zr–B substrate layer were compounded with the substrate layer step by step. After glassing treatment at 850°C for 60 min, this film transformed into a glass lined coating. It was shown from X-ray diffraction analysis that, after holding it at a temperature of 1500°C for 30 min, the amount of crystallinity in the Si–Zr–B coating was about 1–3% (vol.-%). Finally, the undercooling experiment showed that a large undercooling (up to 140 K) was achieved in a DD3 (Ni–Cr–Mo–Al–Ti–Co–W) single crystal superalloy melt in this coated mould. So it is concluded that a Si–Zr–B coating has got a good structural stability at high temperature and provides ideal non-catalytic nucleation inhibition for an undercooled superalloy.     

Effects of different metals on adhesive wear behaviour of alloy surface produced by TIG process

Abstract

Low carbon steel surfaces were alloyed with composite powders using the tungsten inert gas welding method. After the alloying process, the effects of cladding surface on the microstructural characteristics and adhesive wear of the alloyed samples were examined. The sliding wear behavior of samples was investigated in a block on ring apparatus under the loads of 20, 40, 60 and 80 N respectively. In the experimental investigation, a low carbon steel surface was alloyed with austenitic stainless steel powder and austenitic stainless steel powder mixed with 4·5% Co, Mo and Ti particles respectively. Following surface alloying, conventional characterisation techniques, such as optical microscopy, scanning electron microscopy, energy dispersive spectrograph and X-ray diffraction, were used to study the microstructure of the alloyed zone. Examination of the microstructure revealed the presence of M₂₃C₆ carbides, solid melt phases and intermetallic phases, such as Ni₃Ti, depending on the alloying element in the composite. As the amount of the reinforcing material increased, the saturation rates for the samples decreased, while their hardness increased. The adhesive abrasion tests conducted revealed that temperature input plays a significant role on the microstructure characteristics, which positively affected the adhesive abrasion values of the samples. Consequently, the tungsten inert gas welding method was successfully used for the surface alloying of low carbon steels.