A Monte Carlo model for predicting the effective emissivity of the silicon wafer in rapid thermal processing furnaces

Advances in microelectronics led to the development of rapid thermal processing (RTP). Accurate in situ temperature measurement and control are crucial for RTP furnaces to be largely accepted in the fabrication of semiconductor chips. This paper describes an effective emissivity model based on the Monte Carlo method to facilitate radiometric temperature measurements. The results showed that for non-diffuse wafers the “true” effective emissivity (defined in this paper) should be used, instead of the hemispherical effective emissivity, to correct thermometer readings. The geometric parameters and surface radiative properties can significantly influence the effective emissivity. The numerical aperture of the lightpipe radiation thermometer and the wafer-to-shield distance may be optimized to improve the measurement accuracy.     

Flexural strength analysis of non-post-tensioned and post-tensioned concrete-filled circular steel tubes

Concrete-filled circular steel tubes (CFT) have recently gained significant attention for their enhanced strength and ductility over the conventional steel and reinforced concrete construction. The concrete compressive strength is significantly increased by the lateral confinement provided by the steel tube and local buckling of the steel tube is restrained by the concrete infill. This paper investigates the further enhancement of these composite actions due to post-tensioning the concrete cores inside circular steel tubes. The flexural behavior of a post-tensioned CFT as well as a non-post-tensioned CFT was studied experimentally and analytically. A numerical algorithm for predicting the moment capacities of circular CFT, with or without the post-tensioning effects, has been validated against the test results by the authors as well as those published in the literature.     

Measurement of the contact area of a dovetail milling cutter using an ultrasonic method

Since there is no reliable mathematical model to analyze a multi-points contact simultaneously, the most effective way to know the contact area is to use experimental method directly. This study measures the contact area between a dovetail milling cutter and a steel plate by using ultrasound for regional scanning. This is a novel application for milling cutters and has not been applied before. The transducer emits an ultrasonic pulse to detect the contact surface. If contact occurs, the pulse is partially transmitted into the specimen. Therefore, the signal reflected back to the pulse receiver is reduced. The amount by which the signal amplitude is reduced is a measure of the degree of contact.     

Structure, mechanical and tribological properties of diamond-like carbon films on aluminum alloy by arc ion plating

The low hardness and poor tribological performance of aluminum alloys restrict their engineering applications. However, protective hard films deposited on aluminum alloys are believed to be effective for overcoming their poor wear properties. In this paper, diamond-like carbon (DLC) films as hard protective film were deposited on 2024 aluminum alloy by arc ion plating. The dependence of the chemical state and microstructure of the films on substrate bias voltage was analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy. The mechanical and tribological properties of the DLC films deposited on aluminum alloy were investigated by nanoindentation and ball-on-disk tribotester, respectively. The results show that the deposited DLC films were very well-adhered to the aluminum alloy substrate, with no cracks or delamination being observed. A maximum sp³ content of about 37% was obtained at −100 V substrate bias, resulting in a hardness of 30 GPa and elastic modulus of 280 GPa. Thus, the surface hardness and wear resistance of 2024 aluminum alloy can be significantly improved by applying a protective DLC film coating. The DLC-coated aluminum alloy showed a stable and relatively low friction coefficient, as well as narrower and shallower wear tracks in comparison with the uncoated aluminum alloy.     

The structure and adhesion of hydrogenated amorphous carbon (a-C:H) films synthesized on CoCrMo alloy by plasma immersion ion implantation and deposition at different flow ratios of acetylene to argon

Hydrogenated amorphous carbon (a-C:H) film is deposited on CoCrMo alloy by plasma immersion ion implantation and deposition (PIII-D) at different flow ratios of acetylene to argon (C₂H₂/Ar). The results show that Ar fraction in the C₂H₂-Ar gas mixture has an important effect on the structure and the adhesion of the a-C:H films. When Ar fraction in the C₂H₂-Ar gas mixture is less than 50%, the fabricated a-C:H film composition transfer from graphite-like to diamond-like which contains higher sp³ binding thanks to Ar ion bombardment, and the adhesion strength decreased with the increment of Ar fraction. But when Ar fraction in the C₂H₂-Ar gas mixture is beyond 50%, the fabricated film contains more sp² bonding for thermally driven and exhibits higher adhesion strength with the increment of the Ar fraction.     

Beam quality test technology and devices of electron beam welding

The electron beam four-dimensional quality test system was developed targeted at the 5-100 mA electron beam current of a high-voltage electron beam welding machine. The system includes the control module, sensor module, driver module, and analysis software, which is based on the complex programmable logic device (CPLD). The quality test system obtains the data of quasi-instantaneous power density distribution (QIPDD) of the electron beam by controlling the beam periodically, scanning the surface of a Faraday cup. Fixing the Faraday cup at an X- and Y-axis coordinate position under constant conditions, the three-dimensional graphic of QIPDD of the beam about the data of a single cross-section was showed by using computer reconstruction technology. Several QIPDD of the electron beam cross-section at different working distance in axial direction reconstructed the four-dimensional graphics of the beam.     

Isothermal section of the Y-Co-V ternary system at 500 °C

The isothermal section of the Y-Co-V system at 500 °C has been investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Only one ternary compound YV_xCo_12−x with a homogeneity range of 1.30 ≤ x ≤3.64 was found in this system. The maximum solid solubilities of V in Y₂Co₁₇, Y₂Co₇, YCo₃, YCo₂ and Y₃Co are about 10.0, 1.0, 3.0, 4.0 and 4.0 at.% V, respectively. The compounds VCo and VCo₃ have a homogeneity range of 46-66 at.% V and 22-30 at.% V, respectively. The maximum solid solubility of Y in VCo is about 2.0 at.% Y.     

Structural damage alarming using auto-associative neural network technique: Exploration of environment-tolerant capacity and setup of alarming threshold

With the intention of avoiding false-positive and false-negative alarms in structural damage alarming using the auto-associative neural network (AANN) technique, two issues pertaining to this technique are addressed in this study. The first issue explored is the environment-tolerant capacity of the AANN. Efforts have been made to seek a generalization technique to enhance the environment-tolerant capacity. First, a baseline AANN model is formulated using the conventional training algorithm. Generalization techniques including AIC and FPE, early stopping, and Bayesian regularization are then investigated, resulting in three new AANN models. Their environment-tolerant capacity is evaluated as per their capability to avoid false-positive and false-negative alarms. The other issue addressed is the setup of alarming threshold, with intent to reduce the uncertainty in AANN-based structural damage alarming. A procedure based on the probability analysis of the novelty index is proposed for this purpose. First, the novelty index characterizing the intact structure is analyzed by the Kolmogorov-Smirnov goodness-of-fit test to obtain its best-fit continuous probability distribution. A confidence interval is then defined in consideration of the compromise between type I and type II errors. The alarming threshold of the novelty index is consequently set at the upper limit of the confidence interval. The above explorations are examined by using the long-term monitoring data on modal properties of the cable-stayed Ting Kau Bridge. The capability to eliminate false-positive alarm is verified by using unseen testing data which were not used in formulating the AANN models, while the capability to alleviate false-negative alarm is examined by using simulated data from the ‘damaged’ bridge with the help of a precise finite element model. The study indicates that the early stopping technique performs best in improving the environment-tolerant capacity of the AANN, and the alarming threshold set by the proposed procedure helps to reduce the uncertainty in AANN-based structural damage alarming.     

Identification of the effect of grain size on levitation force of well-textured YBCO bulk superconductors

The levitation forces of samples with different grain size have been directly investigated and identified in well-textured YBCO bulks. A single-domain YBCO bulk of ∅30 mm was prepared by a top seeded melt growth process, then divided into two, three and four parts to acquire the levitation forces of samples with different grain size but with completely the same grain orientation. The maximum levitation force for the single-domain sample is about 1.68, 2.05 and 2.4 times higher than that of the samples with two, three, and four grain domains. It is directly confirmed that the levitation force of a single-domain YBCO bulk is much superior than that of samples with multiple domains. It is found that the levitation force is inversely proportional to the total length of grain boundaries of the corresponding sample.