Selective laser melting (SLM) is an additive manufacturing process for the direct fabrication of prototypes, tools and functional parts. The process uses a high intensity laser beam to selectively fuse fine metal powder particles together in a layer-wise manner by scanning cross-sections generated from a three-dimensional CAD model. The SLM process is capable of producing near fully dense functional products without almost any geometrical limitation and having mechanical properties comparable to those produced by conventional manufacturing techniques. There is a wide range of materials that are suitable to be processed by SLM including various steels, Ti, Al and CoCr alloys. Being one of these materials, maraging steel 300 (18Ni-300) is an iron-nickel steel alloy which is often used in applications where high fracture toughness and strength are required or where dimensional changes have to remain at a minimal level, e.g. aircraft and aerospace industries for rocket motor castings and landing gear or tooling applications. To achieve its superior strength and hardness, maraging steel, of which the name is derived from ‘martensite aging’, should be treated with an aging heat treatment. In this study, the effect of the SLM parameters (scan speed and layer thickness) on the obtained density, surface quality and hardness of maraging steel 300 parts is investigated. Moreover, various aging heat treatments (different combinations of duration and maximum temperature) are applied on the SLM parts to achieve high hardness values. The mechanical testing of maraging steel 300 specimens produced by SLM and treated with an appropriate aging treatment is accomplished by impact toughness and tensile tests and compared to the results obtained using conventional production techniques. Additionally, the microstructures of as-built and heat treated parts are investigated.
To the Editor: For persistent mucocutaneous infections due to herpes simplex virus (HSV) in immunosuppressed patients, acyclovir is the drug of choice1. Foscarnet is an alternative agent,2,3 but it too may lead to resistance. A new approach to the therapy of HSV infections is based on the use of an acyclic nucleoside phosphonate, (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC), a potent and selective inhibitor of various DNA viruses, including HSV types 1 and 2 and thymidine kinase-deficient mutants of HSV4,5. We used HPMPC (1 percent, in Beeler base or Orabase), applied topically once a day on three consecutive days a… © 1993, Massachusetts Medical Society. All rights reserved.