They can be, but due to the cost, it's quite rare.
Bicycle frames are sometimes made of materials such as steel, aluminum, carbon fiber, and titanium.
Aluminum,oil,titanium,steel
The most common metal used for standard bicycle frames is steel, although it is possible to get frames made from graphite, aluminum, and titanium alloy.
Usually different steel and aluminium alloys but sometimes also Titanium.
Bicycle frames are made of alloys, carbon fiber, steel, titanium, or bamboo.
Magnesium, Titanium
The stem of a bicycle can be made from alloy, carbon or titanium.
Using a titanium seatpost for a bicycle offers benefits such as being lightweight, strong, durable, and resistant to corrosion. These qualities can improve the overall performance and longevity of the bike.
Titanium is very flexy compared to steel and aluminium.This means that to get nice ride characteristics out of a titanium frame you need to pick tubing diameter and wall thickness real carefully.
Titanium is not made in bombs and is not an explosive.
Either steel, aluminum, or titanium.
The actual bell is usually made out of metal. Steel, titanium, or aluminium will do. The handlebar clamp can be made of either metal or plastic. Sometimes they're even simply attached with a rubber band/o-ring.