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The Ni-based superalloy IN-738 LC is known to be susceptible to porosity and different types of cracking during the build-up process and, thus, challenging to manufacture using selective laser melting (SLM). Determining a feasible set of operating parameters for SLM of nickel-based superalloys involves new approach to experimental design based on the Doehlert method that assists in determining an optimal (feasible) set of operating parameters for SLM of IN-738 LC powder alloy.

The SLM parameters are evaluated in terms of their effectiveness in obtaining the microstructure with a porosity content of <0.5 per cent and without micro-cracking. The experimental approach is exemplified with the Doehlert matrix response variable, relative density, by comparing Archimedes method with microstructural assessments of pores and cracks from image analysis. The effect of heat treatment (HT) and hot isostatic pressing (HIP) on the microstructure of the SLMed IN-738 LC powder alloy has been examined and the consequential tensile response characterised.

By using optimised process parameters (low heat input, medium scanning speed and small hatching distance) which provides medium energy density, samples of IN-738 LC with a macroscopic porosity <0.5 per cent and free of micro-cracks can be manufactured by SLM. The results indicate that HIP of SLMed material did not lead to a noticeable effect on mechanical properties compared to HT of SLMed material suggesting that the level of both porosity and crack density might be already below the detection limit for the mere heat-treated material.

SLM processing parameters (power, scan speed, hatching distance) for IN-738 LC were successfully optimised after only 14 experiments using Doehlert design. Two independent methods, Archimedes method and image analysis, were used in this study to assess relative density of SLM-produced samples with sets of processing parameters showing coherency in prediction with predicted response by Doehlert design.

Selective laser melting (SLM) process is an additive manufacturing method that uses computer-aided design to fabricate complex components layer-by-layer. Surface roughness is one of the primary drawbacks of SLM process; hence, the purpose of this paper is to present a parametric study and optimisation of fundamental parameters, including scan power, speed, inclined angle and layer thickness on surface roughness during selective laser melting of Hastelloy X.

Parametric significance on surface finish was analysed using analysis of variance and response surface methodology. General agreement between predicted and measured values was achieved. Surface characteristics of both up-skin and down-skin with various angles were covered within the investigated range.

Both experimental and statistical analysis showed that surface roughness of up-skin was primarily influenced by scan power, inclined angle and layer thickness while down-skin was more affected by the former two factors. Melt pool shape and staircase size were found to determine the up-skin surface, whereas attached particles were responsible for down-skin surface roughness.

As per our understanding, this manuscript provides valuable insight into the surface quality problem of SLM, which is a very critical issue for up-grading the process for manufacturing real components. This manuscript helps promote improved knowledge and understanding of the attributes and capabilities of this rapidly evolving 3D printing technology. Moreover, it establishes usable processing window and helps obtain optimal conditions, thus offering useful information to professionals working in this field. By combining experiments with statistical analysis, both practice and theory relevant to SLM process are further developed.

Limited research has attempted to reveal the different modes of the melt pool formation in additive manufacturing. This paper aims to study the mechanisms of surface roughness formation, especially on the aspect of melt pool formation which determine the surface profile and consequently significantly influence the surface roughness.

In this study, the conditions under which different modes of melt pool formation (conduction mode and keyhole mode) occur for the case of as-fabricated Hastelloy X using direct metal laser solidification (DMLS) are derived and validated experimentally. Top surfaces of uni-directionally built samples under various processing conditions are cut, grinded, polished and etched to reveal their individual melt pool morphologies. Similarly, up-skin (slope angle < 90°) and down-skin (slope angle > 90°) melt pool morphologies are also investigated to compare the differences. Surface tension gradients and resultant Marangoni flow, which dominate the melt flow in the melt pool, is also calculated to help better evaluate the melt pool shape forming.

Two types of melt pool formation modes are dominating in DMLS: conduction mode and keyhole mode. Melt pool formed by conduction mode generally has an aspect ratio of 1:2 (depth vs width) and is in elliptical shape. Appropriate selection of scanning laser power and speed are required to maintain a low characteristic length and width ratio to prevent ballings. Melt pool formed by keyhole mode has an aspect ratio of 1:1 or less. High-energy contour promotes formation of key-hole-shaped melt pool which fills the gaps between layers and smoothens the up-skin surface roughness. Low-energy contour scan is necessary for down-skin surface to form small melt pool profiles and achieve low Ra.

This paper provides valuable insight into the origins of surface quality problem of DMLS, which is a very critical issue for upgrading the process for manufacturing real components. This paper helps promote the understanding of the attributes and capabilities of this rapidly evolving three-dimensional printing technology and allow appropriate control of processing parameters for successful fabrication of components with sound surface quality.

This chapter reviews the institutional seasonality phenomenon in Asian outbound tourism. Eight key Asian countries were selected for investigation. Secondary data and archives from official tourism authorities and government reports are used as the information sources for the holiday systems and the celebrations for the cultural festivals. Four categories of holidays shaping the outbound seasonality patterns (universal holidays based on Gregorian calendar, Chinese culture-based holidays, religious festivals, and school holidays) are identified across the eight countries. Particular observances for those key cultural and religious holidays are highlighted. The opportunities and challenges for destination managers and tourism businesses to capitalize on and support peak outbound Asian seasonality are discussed.

Over the past three decade, China has established a housing finance system that borrows from the collective experiences of advanced economies. After examining the evolution of China’s housing finance system, the paper focuses on analyzing its challenges and recent changes. The paper argues that China’s highly-centralized financial system prefers financial stability but neglects financial liberalization, and then resulted in severe financial repression, which hurts the efficiency and equality of the housing finance service. After recovering from the 2008 financial crisis via high-cost financial intervention, China took some policy innovations to promote a decentralized finance mechanism, expand finance resources, and support affordable housing financing, through which China hopes to provide a more stable, affordable, and equal housing finance service to help more households own homes.

Propose a more comprehensive explanation on the determinants and fluctuations of China’s exchange rate policy in the past decade (2005–2015).

Case study on China’s exchange rate policies in three respective stages since 2005 and then a comparative study on these three stages.

Put forward a two-pronged explanation on the determinants and fluctuations of China’s exchange rate policy in the past decade and arrive at three specific conclusions. First, external pressure is only one factor among many influencing the formation of China’s national interests (Guojia Liyi in Chinese) and the decision-making process on exchange rate policy. Second, national interest is the fundamental driving force and substratum for making China’s exchange rate policy. Third, in the short term, the specific exchange rate policies in different periods were not always in accordance to the national interests (or Guojia Liyi), due to the influences of some factors on the decision-making environment.

The comprehensive view is conducive to better explaining the formation and fluctuations of China’s exchange rate policy and consequently contributes to understanding and even predicting future policies.