casting of ductile iron with nanoparticles

  • Article Information
    • Title: Comparative study of laser fluence effect on surface modification and hardness profile of austempered ductile iron
    • Authors: Samar Reda Al-Sayed, Haytham Elgazzar, Adel Nofal
    • Published in: Journal of Materials Research and Technology, 31 (2024) 3189–3204
    • Keywords: Laser transformation hardening, Laser partial melting, Laser melting, Laser fluence, Austempered ductile iron (ADI), Microstructure, Hardness, Hardened depth
  • Abstract
    • Investigated the effects of Laser Transformation Hardening (LSH) and Laser Surface Melting (LSM) on ADI alloy.
    • Varied laser fluences (J mm−2) were applied using different beam powers and scanning speeds to optimize hardness, depth, and surface quality.
    • Treated ADI surfaces using Nd:YAG laser in continuous wave mode.
    • Established that laser fluence significantly influences microstructure.
    • Results indicate optimal hardness (900 HV0.1) and depth (184-700 μm) occur at low fluences (9.6-29 J mm−2).
    • Higher fluences (120-360 J mm−2) caused complete melting, increasing hardness to ~1100 HV0.1 and depth to 3.5 mm.
    • Low fluence causes dendritic austenite; higher fluences create cementite plates and retained austenite.
  • 1. Introduction
    • ADI is a unique cast iron developed for enhanced properties over traditional ductile iron.
    • It combines strength, ductility, and fatigue resistance, making it suitable for various applications.
    • Benefits of laser surface engineering include low distortion, precision, and controlled grain growth.
    • Previous studies aimed at enhancing ADI properties through various surface treatments.

  • 2. Experimental Procedure

    • 2.1. Materials

    • As-cast ADI was prepared with a specific chemical composition (3.6% C, 2.0% Si).

    • Samples underwent austenitization at 900 °C for 2 hours, followed by austempering at 370 °C for 1 hour.

    • 2.2. Laser Treatment Setup

    • Nd:YAG laser (max power 2.2 kW) was used for treatment.

    • Key parameters recorded include laser power, scanning speed, and laser fluence calculated by (F = P / (ν × D)).

  • 3. Results

    • 3.1. Microstructural Investigation

    • Analyzed microstructures using optical microscopy and SEM.

    • Treatment at low fluence (9.6–29 J mm−2) resulted in hardened layers with microcracks due to thermal gradients.

    • Medium fluence (37–112 J mm−2) induced partial melting leading to dissolution of nodules and formation of various phases such as martensite and retained austenite.

    • High fluence (>120 J mm−2) resulted in complete melting, forming a homogenized microstructure with different characteristics (e.g., ledeburitic structures).

    • 3.2. X-ray Diffraction Analysis

    • XRD revealed the phase composition varied based on laser fluence, showing peaks for martensite and cementite in treated layers.

    • Insight into structural transformations during the laser treatment process was gained.

    • 3.3. Hardened Depth Profile

    • Higher laser power increased hardened depths, inversely related to laser speed.

    • 3.4. Microhardness Measurements

    • Hardness increased significantly with higher laser fluences, showing depth-hardness profiles varied with treatment conditions.

  • 4. Conclusion
    • Utilized a broad laser fluence range to assess microstructure and hardness of ADI.
    • Identified three main processing methods: laser hardening, partial melting, complete melting.
    • Established that hardness increased with fluence and depended on the microstructure's phase composition.
    • Noted that laser speed impacts treated thickness significantly more than power, with the deepest layer (3.5 mm) recorded at high power and low speed.